I have used two Owens Products diamond plate aluminum ATV boxes on the roof rack of my LJ for four and a half years. They carry recovery gear, trash bags, spares, a machette, tools, you name it...
The boxes feature locks and padle latches like a pick up tool box and gas strut lid supports (one of each of the above per box.) I thought they might leak, but the have stayed dry in even the heaviest of down pours while I'm driving 70mph, in feet of snow, through the truck wash, etc.
The boxes are attractive in appearence, offerred in bright aluminum and black powder coat (which has held up without flaw on mine) and offered in three sizes, small, medium and large. The boxes themselves are relatively light.
The ones I use are the smalls @ 32"lx12"wx6"h. They are bolted to my rack through the bottoms with rubber grommets for seals.
Medium boxes measure 34"lx12"wx9"h; large boxes measure 35"lx12"wx12.5"h.