We started with 40' and eventually moved up to 43' with no regrets. Sure, there are some state and national parks where you'll be too long, but if you can live with that, then by all means do it. The longer, heavier coach with tag axle is better equipped to handle crosswinds.
Last June, we went from AZ to IL and all I planned was the route. We had no problem finding a place to park each night. I just drove until I felt like stopping and found an RV park with full hookups within an hour.
Good luck with it :)