I used a 3/16" thick by 5' wide steel plate with 4 bolts going thru the box with blue thread-lok an nylok nuts on the bottom. bolts are just long enough to not hit the paint below by about a 1/4"
I mounted the plate under the inside 4 rops hold down nuts. I put 3/4" holes in the plate to have a little play room. I then put the seat where I always keep it for my comfort an then mouted the 50 cal box about 1/4" behind it, so the lid would open without hitting the seat. It worked out great, you can put a lotta stuff in a 50 cal box if need be.
Oh yeah, I put a piece of house carpet in the bottom of the box to keep some of the rattles down. I had to paint the box ford gray, I ran outta kubota gray when repainting the rops an mtg plate.
I think the new "Surplus Center" catalog I got today has them (50 cal box) for 9 or 10 bux on the very back
cover
The pvc schedule 40 4" pipe is munted to the rops with 2 stainless steel HD hose clamps that they use underground on plumbing equip. The only diff is that the screw in'em is SS also.
I have an all SS Rambo knife mounted to the pipe also for any unruly snakes an etc
Gotta figure out where to mount my snake shootin' gun/revolver on it next.
Will get some pics of the weights I put on the frt end yesterday also. Always another project. I needed them for going uphill on the road with a 42" brush hog in the raised position. It will get a little lite in the frt end if not for that extra 100 lb. up there