I have used spray foam numerous times in walls of homes, RV 's and toy haulers, cargo trailers, boats and other applications. I can say that I haven't used it in any military vehicles as of yet...that will be forth coming though!
I agree that once you spray it in, it is a PITA to work with after the fact if you need to do work in between the walls. That is why I try to plan out everything first, like wiring, plumbing, cabling, to go inside the walls, ceiling and even floors before I spray. Sometimes I also run a unused conduit pipe throughout the walls to tap into, in case something does come up in the future.
I have used both, open and closed cell spray foam in the past. I have only used the open cell foam one time and was not happy with results in my application but it does cost less then closed cell foam. Now only use closed cell foam because of it characteristics, and specifications that come from the manufacturing companies. It has been my experience that closed cell foam will not absorb or hold moisture since it is closed cell, and that it is like glue and sticks to almost everything after it expands and cures...wear gloves and long sleeve shirt. It is the best insulation moisture barrier I have found to date.
If you used it and it expands to the outside anywhere, trim it, paint or coat with UV barrier because it does not like long term exposure to UV rays.
Of course if you get any damage to the panels or exterior skin, after installing the foam, then you need to attend to it ASAP so moisture doesn't pool of lay inside the damage area.
Just my 2 cents,
Take care, be safe,
Tom.