Last year we went from a 36' fifth wheel to a 45' Class A and started fulltiming. We just spent our first winter in the Southern US. We traveled from Alberta to Alabama to California and are now headed back to Alberta.
As someone previously mentioned, you may have to plan ahead just a bit more to find a campground, but we have really not had any problems with roads or campgrounds. Some of the older campgrounds may be a little tight.
We don't feel like we have missed out on anything by having a 45' coach.
As for the roads you are not allowed on. They will be much more enjoyable to explore with the towed.
The little bit of extra hassle caused by a 45' coach is more than offset by the additional living space it provides, especially for fulltiming.
If we had to do it all over again, we would still end up with a 45' coach.
Also Congrat's on the recent retirement.