I haven't read your post yet and may edit this after I do, but I don't think the atmosphere would be much different than what he's already used to, it's just a normal planet like any other inhabited planet in the galaxy right? And if your a human why would you need an air pack? Mandalorians are humans too.
Well...acctually Mandalore and it's neighbouring systems are supposed to be harsher than most inhabited planets arn't they? I do remember reading somewhere about the harshness of the atmosphere or something.
Okay so I guess then that the atmosphere would be harsher than what he's used to but not unbarable or requiring an air pack. It would just be a little tough to breathe.
It wouldn't make sense for the Mandalorians to have air packs that you might use since they normally breath their own atmosphere's air.
I think you'll just have to suffer a little. What won't kill you will only make you stronger.