It is much easier to back a 30' motorhome into the average western states campsite than a 30' trailer. I have been impressed in particular by the Class B+ Phoenix MH (built on the Ford E-450 chassis) with the double slide-outs.
The 5th wheel trailers will require a heavy duty vehicle and involve a lot more steps everytime your wife goes in and out as well as getting up to the sleeping area. The 5th wheels work well when you are planning to stay in one place for weeks at a time and can unhitch the tow vehicle and use it for personal transportation around the area.