We have a 45' MH and do all the things you'd like to do except roaming around California. I've looked at the Caltrans requirements for a 40-45 MH and they are very restrictive. You can only drive a mile off an approved road for gas unless you see a certain sign. We did take a chance and go to Palm Springs and were not stopped but I figured with all the high end parks close to the highway it would be OK. Other then that, I would be wary of California.
In the last 3 weeks we have stayed in 2 National Parks, 2 state parks and a National Recreation Area. We fit fine in all of them. Oddly enough the tightest spots were in private CG's. I love COE CG's. We do stop in Casino's, rest areas and Walmart's. We can go a couple of weeks if we run the genset twice a day for 2-3 hours. If we need AC, we need to run the genset while stopped. Running down the road we can run 2 AC's off the alternator, battery and inverter combo.
There is no question 45' is bigger then 37'. The extra length offers certain advantages while coming with some disadvantages. Only you know how to weight the trade offs.
