i tried those reversa bits but those bolts do not come out easy. i ended up drilling the 1 that broke out and replaced it with a stainless nut n bolt. that work fine but its a pain it the but drillin it out!
You can always go under it and turn it with a pair of pliers but if its rusted then drilling it is the only way to do it. I had to do 2 in my tub for the back seat and they were rusted solid. The guy before me had rhino lined over 2 that he cut and when I finally got a back seat to put in it, I found them cut off flush. I ended up using a drill but smaller than the bolt itself but broke one off in the bolt. The the dremel with a cone shaped solid grinding wheel came out. 2 hours later they were out and hadn't messed up the threads on the factory nut welded to the tub. Have fun!
Do you have a big hammer and a chisel? Those things are in there good. Seriously though, get 1/8th inch cobalt enhanced drill bit and start a pilot hole, then move up to i'd say a 5/16th and just start drilling on that sumbitch.