I have to get them off and I'm sure any of you who've replaced a bumper or fuel tank know how little space there is to get these off. Furthermore, mine are rusted BADLY.

Is spraying PB Blaster around the bolts for 48 hours and praying the best thing to do?

 

my front bumper brackets were rusted too but i got em off easy without pb. very tight space to remove the bumper though!

 

Is it the rear ? I had to heat and I mean HEAT these bolts inside the bumper just to get about 1 turn out of end with a rachet-wrench through the sides ( they look like they are self locking considering the look of the threads ). If your not gonna use the bumper again you can use a holesaw where the bolts are and get them straight on.