Are you sure you want a 5th?
With a 36 ft you should be able to get in most state parks. But most state parks aren't like Texas. You will find many that have no hook ups or just electricity. National Parks are worse. I have decided they do all they can to discourage RV's. Short sites and few hook ups. You may find yourself staying in expensive private RV parks outside the big national parks. Or, being forced to stay in cheaper rundown trailer parks. The exception is US Corps of Engineers parks. They are usually at a COE site like a lake. Hate to sound discouraging, but that is my opinion.
I would look at a medium size motor home and flat tow a small,car. Heavier duty chassis that is designed by Detroit engineers, not accountants in Elkhart, IN.
I have a 36ft 5th wheel with a truck that is pushing 55ft total.