Sounds like a good way to handle things, and build up a small amount of equity instead of paying rent.
Have you looked at any? There are thousands of models to choose from--begin by finding an RV show to go thru some of them. You have the 'required truck'--that may or may not be correct, if you opt for a larger fiver.
Since it is for full-time living, you should seriously consider a fiver with space/connections for a washer/dryer. Also, living in a fiver, a large fridge (over 10cuft) is almost a necessity. If you will be stationed in a hot area, need 2 ACs, not one. Once you figure those needs out, then it will come down to what you/she like and price.
Do research on the internet for the owners group forums for any brand you are considering---lots of info there as to how each mfg builds them to last-or not.
Be careful of getting too excited over appearances more than quality. Also, consider a newer used unit instead of a new one--getting a new one does not insure that you get one without problems.
If you want to compare prices on used units: www.pplmotorhomes.com
Both of these websites have a world of info on pricing and floorplans. Don't be misled by the motorhomes in ppl, they handle all types, nothing new.
Wish you the best of luck.
And welcome to the forum.