You don't need sealant. Just clamp them.
I suggest you remove the old exhaust and slap up the trubendz pre assembled (w/out clamps) and get everything in its hangers. The adjust and use clamps as you get everything where you want it. THEN it wouldn't be a bad idea to go to an exhaust shop and have them weld it, or if you want to weld it yourself, drop the exhaust with clamps tightened, then weld, and remove clamps and put it back up. I am still running clamps on mine, with no leaks or issues of any kind.
