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RvSearch.com for many floorplans and lengths. Don't go specific on your mileage from home just yet, look at units that will work for you. Then try to find one close to home or someplace like Yellowstone, where you can drive out to look at it, then vacation on the way back home.
I agree that a 26 or 28' overall is better and easier to park in a National Park. My 30' motorhome limits me to only a few dozen sites in a 120 site campground. I was in a 40' Country Coach in Sequoia National Park and finding a site to accomidate the RV and Jeep we towed was really difficult, I had to rent a additional site for the Jeep. I pulled into the first site I could on mid day Friday, and then went looking for a better site, did not find anything else that looked like it could handle the 40' RV. So I was really lucky.
Had it been a trailer, there is no way I could have backed it into that site, it was way far away from a cross street, and would take 1/2 mile loop to get out to where it could be turned around again, so getting out on a one way street through the campground loop would be impossible.
At least with a motorhome, you can pick backing in or drive in. I prefer backing in, because normally the rear overhang is so much longer, you can back over the bumper stops at the rear of the campsite, and stop when the tires reach the bump stop. With a travel trailer, pulling in and leaving the truck hooked up is rarely a option on a 40' long site. Parking the trailer than pulling the truck along side is rarely a option on a pull into site, especially when there are specific rules against pulling onto the grass, or as in this site, a cement weighted down cement picknic table right in front of the parking pad. Other sites had rocks - 3' diameter to prevent you from backing over them, and parking a longer than normal RV on the 20 - 25' long paved parking pads.
Once you find a unit, say a Cedar Creek, write back. Ask "How does Cedar Creek compare to other travel trailers" and you will get several responces. Some RV manufactures have gone really cheap. The Cedar Creek that I was in was top notch for a fifth wheel, and they are one of the better built units.
I like my97 Fleetwood Bounder, and toured the factory twice before buying it. Took a tour again after it was a couple years old, and saw many nice things about it. They have a channel near the ceiling on each side, where wiring is run at the factory, easy to get to for repairs, and easy for me to install new wiring to run a 1,500 watt inverter, and install a TV camera, and several other things. You might want to look for this feature on any RV's you are looking at.
Also my RV has both 12 and 120 volt wiring to the rear bedroom, so it is possible to install a second A/C. What I did was replace the noisy bathroom fan and the kitchen and bedroom manual vents with fantastic fans, covering them with Maxx air vents, so that I can leave them open in the rain, nothing will get inside. The vents are also 17 years old, without cracking the plastic covers. The Maxx Air covers seem to hold up to the UV rays very well.
Fred.