Heat, pb blaster and patience are your friend. An impact tool of the air type or hammer type may help as well but use short bursts to try rattling them loose rather then twisting the head off or spinning the tool.
I think most of them are torx size T45. I found a cheap set of bits at autozone that included a size T47 and I was able to pound that in and get mine out without stripping. The good news is that if you have to drill they are not too hard to get at from the bottom.
All you need is heat and a good impact. I just took my roll bar out of my '93 last week. At first I tried to just use my impact, but none of them would budge. I then used a torch to heat the bolts from the backside (everyone is easily accessible), and then hit them with the impact again...they all zipped right out with out any trouble. The heat is by far the secret IMO. I think there is some factory thread locker on the threads and the heat loosens it. Also the impact is important because you can put a lot of downward pressure on the torx so it wont strip out. Often they strip simply because people use a ratchet and don't use enough downward force. One last tip is to make sure there is no factory "caulk/sealant" on the threads. On my Jeep they went crazy with the sealer and it was on the threads of a few bolts, so I used a wire wheel on my dremel to clean it off before I removed them. Good luck!
If you don't have access to an impact or welder (like me) - use a dremel to cut part of the head off on opposite sides. This gives you two flat surfaces. Then heat with a torch, then put your vice grips on and presto - it will break loose. Had to do this on six of my roll bar bolts yesterday. Worked every time.
A Rancher told me that back home he can drive his Jeep all day and not get off his own property; I said "I've got a Jeep like that too"!
"Nothing sucks more than that moment during an argument when you realize you're wrong" (Paul :-̃)