Need ideas for how to mount ammo cans for bags

[deadman13]

i bought 2 .50 cal (?) ammo cans to turn into saddle bags of a sort, as i was going to mount them using the 2 fender bolts as mounting points. well i got them home, and i came to realise that in order to clear the shocks, i have to move them so far back that ill only be able to use one of the fender bolts, and thats just not enough. i also have removed the rear seat and dont plan on seeing it unless i make a back rest ( if i could ever get the other pictures of that how-to to load up.) and so that bolt hole is free.

i know how to make them rattle proof, just not sure as to how to mount them up and keep them sturdy. thanks all in advance!