You'll need to fabricate your own suspension frame for them, or modify an existing one that will work. It'll take some doing. Most installations consist of simple brackets permanently bolted to the bike, and the cans. You could make a locking system but you're looking at some engineering and experimentation, and that usually means time. I would guess it would take the average backyard mechanic about one to two hours to rig up a bolt-on mounting system, and about six hours to work the bugs out of a locking/removable system. Access to a welder would be awesome but you could hacksaw and bolt your way around it if you had to.

.50 cal ammo cans are about 14''x16''x7'' ... if you think you need more than that, maybe you oughta get a sidecar and a trailer? haha

I made a hard 'T-bag' case for a bike once, out of plywood. It had a locking lid, weathertight gasket, and a locking system to keep it on the bike which used the same key as the lid lock. It was alright. Got the job done, cost less than $40, looked alright. But it was pretty heavy for it's size. I figure it took me about 8 hours total, but a lot of that was finishing and painting.