3000 members? Wow...
I don't know what to tell you about ammo cans. I found a couple of them on ebay a while back, and was going to fit them to my 08 KLR, but I found them to be pretty heavy, for a relatively small interior space.
The ones that I found were the plastic ones. If you could find metal ones, they might be better.
You might try Googling for surplus materials.. you could probably find out what shipping costs would be on google as well.
I wish I could tell you more, but I just don't know. Good luck with your search.
You need to post some pictures of you and your group... show us the roads you guys have to ride on over there.