I keep a tensioner, idler pullies, extra belt, and a few basic things to address those.
My experience has been that those are the simplest, worst things that can keep you from moving so far.
The space under the passenger seat is empty for a reason I believe!!
When we head out, I just look carefully over everything, I'll be doing an oil change, fuel filter, checking belt and tensioner well, I'll probably go ahead and pull the belt off and inspect pulleys carefully for anything that looks suspect.
Having two sprinters is nice - especially when one is full time use and the other is part time leisure - makes for a nice "parts house on wheels" scenario!! I know this isn't practical for all, I was in the right place, doin' the right thing at the right time...