How big of trailer or 5th wheel you get will depend upon your lifestyle. If you want all the amenities of home, than a big one will be required. If you intend on dragging out area rugs, lanterns, coolers, games etc then the big ones are needed. If you need a place to eat, cleanup and rest after a busy day then a smaller one (under 30') should do, especially if you move frequently and plan on spending a lot of time in State and National parks and forests.
As far as getting into a high cab, do as I did my in-laws, carry a wooden box about 6 or 8 inches high by 14 x 18 inches for stability. Set by the door and it "lowers" the truck 6 or 8 inches.