Have you done the research on how much it will cost to rent an RV in NYC and drop it in Las Vegas? Or, if you can even do it at all?
My plan would be to take the Amtrak Empire service from NYP to Buffalo/Depew and take a tour to Niagara Falls.
Get on the Lake Shore Limited from Buffalo (leaves at midnight) and go either to Elkhart Indiana or Chicago. There are still RV's manufactured in Elkhart. You might get lucky on finding a place to rent and stay there.
The parts that I know of the old US 66 that were not wiped out by I-40 are from Seligman AZ west to Kingman. If you don't go to the Grand Canyon, you can go to the Grand Canyon Caverns near Nelson.
Between Kingman and Las Vegas you will go over the new bridge high above Hoover Dam. Take the time to drive down to and over the dam. Park on the Arizona side of the dam in the second lot which is free.
After you see Las Vegas head south on US 95 back to I-40. Going west on I-40 the first exit will put you on the National Trails Highway through Amboy which many people call "Radiator Springs" from the movie Cars.
There is a Rt. 66 museum in Victorville across the street from the railroad station. The old Rt. 66 went over the Cajone Pass where I-15 is now.
You will be able to rent a nice car in Las Vegas but I am unsure about your plan to drop off an RV.

Have you been to the US before?
If not, then IMOP, this is a huge huge mistake.

Finding campgrounds for your RV should be no problem outside large cities.

It is shorter to cross through Canada from Niagara Falls to Detroit and on to Chicago than going around via Cleveland, but you need to check if you can do that with your rental.

Nope never been before myself. Yes rv already booked and paid for!

Do you have experience driving in the US?

The trip is not impossible. I've had European relatives who chose to drive cross-country when spending only 3 weeks in the States (one week on the East coast, one on the West coast, and driving in between) who felt that it was worthwhile. Age is a factor, although my parents did it with less travel time when they were close to retirement and thoroughly enjoyed it--it was the only time that they saw any parts of the U.S. between the coasts.

Having never been I don't have any experience here, my two friends have been but have never driven here.

However myself have driven on the opposite side of the road countless times throughout western europe.

March can still be wintry in the northern bits which can cause some major RV issues. A road trip by car would have been easier- but what's done is done.

I would forget about Niagara Falls and Chicago myself - I'd head south and across the southern US.

janisj is correct about March. I recall that a snowstorm to end winter was not uncommon when we lived in Michigan. The weather can be raw. The OP should consider a southern route and look for Rte 66 past Joplin, Missouri.

I would think you will face a few challenges trying to find places to park in the cities/at the sites you will be visiting (except the Grand Canyon).

You're not likely to be able to leave the vehicle at an RV park and take public transit, and finding a lot or garage that you can navigate with the RV might be a stretch. In fact, the simple acts of pulling into and backing out of parking spaces might be more challenging than you anticipate!

Your plan is ambitious to say the least.

We live in Colorado, and travel 5 a solid months per year in our RV. I hope you'll believe me when I tell you that you really need to rethink this plan.

You're wanting a tiny slice of America, and in 24 days you can do that. An RV is an interesting way to travel America, but not an easy one. Even an experienced RVer would be unlikely to attempt the trip you've outlined.

Please realize that it's often not possible, or safe, to just find a place and stop for the night. That's especially true in large cities. Even if you do find places to "boondock", you will need to deal with getting water and dumping the sewer tanks. The easiest way to do that is to stay in pay RV parks.

Another thing to consider is what do you want to DO? The places you've chosen are on the map, but not exactly the highlights of America.

If you decide to do the RV trip, I strongly urge you to head south. Maybe spend a day or two in Washington DC instead of Chicago. It will still be wicked cold, but DC has TONS of things to see and do. And yes, plenty of bars.

Then maybe go down to Nashville, where you'll find a whole 'nother slice of American life and plenty to do.

Then I guess drive I-40 across the country. It's not going to be too exciting... There's just not a lot do DO in these places.

Just west of Albuquerque on Route 66 is a casino that will allow you to park in their parking lot overnight for free. Of course, they'll gladly take your money inside!!!

At the Grand Canyon, you need to go to the south rim. It will be COLD in March.

When you get to Vegas, you cannot just park anywhere. Samstown has a good RV park.

When you rent a car after leaving Vegas, think twice about spending the money for a convertible. It's not THAT warm in March. And I'd recommend going to San Diego rather than LA. There's tons to see and do in San Diego and it's much more manageable than LA.

If you decide to stick with this plan, I'd highly recommend going to the Trailer Life forums. There you will find chat on RV travel and plenty of experienced RV travelers.

forums dot trailerlife dot com

Your plan is ambitious, but doable. I would want to see much more in the west raather than spend all those days in Las Vegas. There are wonderful National Parks, like Zion, Bryce, Arches, Canyonlands, Death Valley, Yosemite to name a few that are awesome and real where you could camp inexpensively.

If you do go to Niagra Falls, make sure your insurance and rv contract let you go into Canada which has some of the best views of the falls.

re emalloy's post - In March one can't get to Yosemite from Las Vegas w/o taking a looooooong/ugly/boring drive through Bakersfield and up the Central Valley.

re jarand's excellent advice/info . . . here is the actual link forums.trailerlife.com

Comments from one who has covered the U.S. over many years...including RVing...now in Boston area moving from Missouri.

I would question renting a camper for such distances. Your proposed route is OK but too much time in Vegas, maybe LA. Need pauses for seeing sites along the way, like Amish country in Penn. and wonderful Chicago museums and Lincoln museum in Springfield, IL. Not much of Rte 66 left, even past Joplin, just a few vintage buildings. You are going to see lots of hills and fields.

Niagra Falls is one of those marvelous sights. Grand Canyon only needs an overnight unless you venture down trail. Good luck in plans.

While I admire your plan, the time of year could make this trip difficult or even dangerous. I would not look forward to driving an RV from New York to Chicago in early March as the weather can be very uncertain. In Pennsylvania, we've had some of our worst snowstorms in early March. The saying goes, "March comes in like a lion and out like a lamb." While you never know what March can bring, consider this while making your plans.

I have to second the advice of jarand when recommending a more southern route across the US or perhaps put off the trip by a month.

If you head south thru NJ, past Philadelphia, Baltimore and DC, through Virginia and into Tennessee (perhaps a visit to Memphis) you'll reach "spring" faster. Then on thru Oklahoma where you can resume your original journey. While near Albuquerque I would suggest a detour to Santa Fe, NM. Also, I would cut a day off of Las Vegas and head through Death Valley.

Good luck with whatever you decide.

Not sure the OP is still around - hasn't been back since the day he started this

You mention St Patrick's Day - which means you will be coming in late winter/very early spring - and it's likely to be a lot colder here than where you are.

I'm not even sure it makes sense to go to Niagara Falls - since many sights will not be open - too early in the year and you could still have substantial snow. (The blizzard of '88 dropped more than 2 feet of snow as far south as NYC at end of March.)

It seems to me that taking a massive vehicle out on the roads in snow and ice is a truly foolhardy venture - even if you can find someone to rent you one. (Have you checked the price for this?)

Also - if you take the southern route the weather will probably be milder - but anyplace north - or in the mountains - you are likely to still get winter weather and some roads through the mountains (and places inside national parks) won;t be open yet.

Strongly suggest you reconsider this:

First - look at late April or May to avoid winter weather

Second - why an RV? Difficult to find places to put them, can;t take them into cities (no place to park) and probably a lot more expensive than renting a car and staying at inexpensive motels.