Earlier I had posted that I use a Moose Fender pack. This pack rocks won't fall off etc, etc, . It is designed to carry a spare tube so it's a little thin and oblong but it holds a fair amount of tools.
I just bolted a nice Moose Fender bag on the back of my KDX-200. The bag was a gift last xmas (99xmas) for my RM but it didn't fit right the RM's fender is too curved. It fits the KDX perfectly. It's about 3 times the capacity of the original, it's taller wider etc. I don't think it'll be a problem mounting the bike but I didn't try it with boots on. I can carry just about all I need in it and then some :)
I can post a photo if you want. I think the bag was about $40.00