I plan on being on the road full-time, ... will be headed to AZ for the winter to bike and live in a van. Next summer I'd like to be up in Idaho, Oregon, Washington, Utah, Montana area. Now that I am looking, a portable shower and toilet would be ok. Ideally I'd like to find a van with all of it with a short wheel base since I'm 5'1" and need a shorter van to drive. I'm now leaning towards finding a promaster.
If you're into biking, definitely go the van route, and make sure you have room under the bed to keep your bike(s) inside the van. Hanging a bike on a rack is just asking for it to get stolen. If you're into winter sports too (like skiing), you bike(s) get covered in road grime driving to and from the mountains in a van.
My wife and I lived full-time in a van mountain biking and skiing for a year. We had a fairly simple DIY build-out. A few tips...
Since you're 5'1, you should be able to sleep cross-wise in any of the new euro-style vans. Get the high roof, (or mid-roof in a ford transit) build a cross-wise bed high enough to easily fit bikes under (we went 39" or 40" of clearance under our bed, but I ride an XL frame... with a smaller frame you can probably get the bed lower). With a cross-wise bed, you should be able to have plenty of room with the shorter wheelbase versions.
For a toilet, we did a luggable loo lid on a 5 gallon bucket lined with trash bags. If you're a guy, keep it for emergency poos only, and work out a pee bottle system for midnight wees.
For a shower, we did a p-fit black card membership for $20 a month, and just wiped with baby wipes or rinsed with some fresh water if we were really sweaty and couldn't get to a shower. YOu mentioned AZ... we spent some time riding in Flagstaff, Sedona, Prescott, North Rim. I can't remember what we did for showers (don't think there's P-Fits anywhere there), but touristy-outdoorsy areas like Sedona usually have campgrounds that will let you shower for $2 or so, even if you're not staying there. You could get a solar-shower-type setup and be fine... plenty of free boondock camping in Az.
Wintering over in northern AZ can be colder than you'd think... much of it is at higher elevations. Can't speak to southern Az...we were there in April and May and didn't go any further south than Prescott. We got 6" of snow in mid-may while we were in the flagstaff area.
Other people have poo-pooed the promaster, but you can't beat the price. We had a 17 year old sprinter and while it was mostly dependable, dealers were few and far between, parts were a pain in the ass to get and expensive, and no independent mechanics knew anything about working on sprinters. Promasters won't have any of those problems, and they're the cheapest of the eurovans on the used market.
Again, having your bike inside the vehicle is 100% requirement for full time, in my opinion, and van is the best way to do it.