1998 V70XC

After dropping my propshaft for the second time, a small problem is starting to turn into a bigger problem...

There is a bracket under the car that holds up the propshaft at the bearing (and supports the exhaust). This bracket is held in place by four bolts. The bolts thread into inserts that are be pressed into channels under the car. With enough salt and grime (which we have plenty of here), the torque required to unscrew a bolt will exceed the torque required to pop the insert free of its seat - allowing the bolt/insert to spin freely without loosening. This had been just one corner last winter (which was still tight enough to not be a problem). It is now a problem at two corners, with one being quite loose.

Is it possible to get at these inserts to keep them from spinning? I think it could be fixed with a cutoff tool & a welder, but don't really want to start down that path.

Thank you.
-Nate