Not trying to insult you - but have you done any research yet into how to spread the load correctly for a roll bar when attaching it?
You need to distribute the load in case you really do go over, otherwise the bar will punch through the sheet metal & possibly (probably) cause injury to occupants of said rig going over.
At a bare minimum you need to weld plates parallel to the floorpan to the bottom of the bar ends, then use a backer plate of decent size & thickness (I like 1/4" for both sides) as a large washer for your bolting surface on the other side of the body (underside).
Also, these are critical welds, not the place to do your first bead. If you have a welder buddy, buy him a few frosties after he does the work for you. Pay for it otherwise, it's really that important.
If you look around you'll see what I'm saying.