I'd like to mount a cargo box on the roof of our RV to have some additional storage. I'm thinking of one of the boxes from Thule, Yakima, etc. that normally mount to a roof rack on a car. We have a '94 Tioga Montara. How would I go about fastening it to the roof? Can I mount it directly to the roof with lag bolts or something like that? Since people mount satellite dishes, etc. on the roof I'm guessing that it's possible to bolt things to the roof, but are there only certain places that are strong enough? Any suggestions or information would be appreciated.