Our club is in a barracks and while we welcome civvies and have a couple as students, the main reason apart from enjoying it that we do MMA is that the military students can still train. We have no curriculum so can train according to whoever we have in. We can have students come in for a few weeks then they disappear for six months or more on deployment, we haven't, touch wood, lost a student yet but one of our pro fighters is a PTI at the Infantry Training Centre and is from 2 Para who took so many casualties, the younger ones were all his trainees, a couple of the older ones were friends.
I've just started a TSD class for adult beginners, the students I have are from a tank regiment (The Queens Royal Lancers, the Death or Glory boys), they're doing their tours as squadrons, the guys I've got have done theirs (they lost two soldiers) so I'll have them for 2 years before they go to Germany permanently. They still have duties though. Sometimes I have a few sometimes none, makes it hard to get the training in for grading. We are hoping a couple of them will manage their black belts or at least red so they can start a club over there that we can go across to and help train grade etc.
We can only run the club though because I am permanently stationed here (I hope lol) it would be very difficult to do so otherwise. I've seen other things like scout groups etc close on other camps because the leaders were posted and there was no one to take over, usually though you could persuade a parent to train and take over until they in turn were posted. Much harder with something like martial arts to find someone to take over.
An MMA club is a bit easier to keep going as you can find martial artists from all disciplines to come and train when they don't have their own clubs to go to. Gradings and lessons aren't a problem, you get a group of like minded martial artists and get to keep your hand in at least.