Can you get a grinding wheel in there? Weld a nut, or have somebody weld a nut on there and try again?

 

Heat may help. They may have threadlocker on them and require a decent amount of heat from a small propane torch. The heat will also help wick the PB blaster down the threads. Use a 6 point socket or box wrench instead of an open end wrench to prevent rounding. ETA: Should be 8mm. I avoid air tools. At least for the initial breaking free.

If they are completely rounded then vise grips or channel locks? Kind of a tight spot though.

ETA: Last ditch would be to use a reinforced cutoff wheel on a Dremel to take the head off carefully. Once the straps and joints are out of the way, more heat and PB and the grip the stub TIGHT with vise grips and rotate out.

 

Multiple tests confirm PB-Blaster is absolutely the worst for anything needing a penetrant. It's barely better than WD40. Instead try Kroil, Liquid Wrench, or PB-Blaster in that order. Give those bolts several drenchings over a day or two.

 

Project Farm did a episode on this and found out Liquid wrench was the best.....Who would have ever guessed......but i like the smell of Aero Kroil

 

Use a torch to heat it up, should break loose.

 

X2 or a torch. Heat is a miracle worker for seized hardware.

 

Try putting an extention or fat punch up against the bolt (in-line with the bolt) and giving it a few hard hits with a BFH.
The jarring along with penetrating oil may help.

 

Apply heat - it's the locktite.