There are many spas kept outdoors and it shouldn't be an issue, just make sure you communicate that with the sales person. I would think if you had an above ground pool with a frame (as opposed to inflatable/stand up size) you wouldn't have any problems keeping the tub filled. There may be issues dealing with the surface/support pad for your locale, as well as water supply (even if delivered, can it fit) and electricity/power unless you are planning something like a Snorkel stove (submerged wood burning option). Unless it is right outside the house while building a structure I would try to include some degree of an outside shower, the cleaner you are before getting into the tub the longer you can keep it going with chemicals and basic maintenance. Your dealer should be able to tell you how to prep for your winter absences.
I would say the biggest thing to look for is the ease of getting in and out. I know when I was younger I could hoist myself up and over and out of things but these days I'm looking for steps or at least comfortable secure ladders. People may be embarrassed by checking out toilets and bathtubs but make sure you get something that will work for you by getting into it before you buy.