for what it's worth, i've never had success with pbblaster. and since i've stripped my boat down to the hull, so i've had to free plenty of stainless bolts. the only things that've worked for me
1 nut splitter
2 impact gun
3 heat
4 drilling
if it's a chunky bolt with a nut i'll split the nut and pull/hammer the bolt out. if it's not a thru bolt, an impact driver usually frees it or snaps the head, in which case i end up drilling the bolt out anyway
heat seems to be the least damaging with varied actual success. if i have a lot of room i'll use a blow torch to heat the bolt/screw. if less room you can get pencil tips for the blow torch, makes all the difference.
otherwise if you have a heavy duty (100w+) soldering iron, you can hold it directly on the bolt/screw. takes awhile though, but does work sometimes and if there's a lot of wood around the fastener sometimes the safest/least damaging. there's a fancy induction bolt heater that mechanics use that i envy, but the $1k price tag was not.
drilling is the fall back, which i've sadly done a lot. just get a center punch and good set of cobalt drill bits, doesn't take too long
the only thing pbblaster ever did for me was make my hands and the surrounding environment stink