Both of mine are rusted out, and I’m guessing this is a common problem, how did you guys go about fixing your’s?
I just fixed mine today, I was going to fiberglass the mounts into place since I was glassing my tire well for a sub enclosure, but it just wasnt necessary,
If you Still have enough metal left, You can run some sheet metal screws through the plastic mount and into the sheet metal in several places and it will be more secure than it was when the mounts were intact, just make sure to get all the cancer , and shale off and paint/undercoat whats left of the remaining metal there. It may be a little trial and error to get the mounts where they should be since you’ll likely lose a bunch of metal when you clean it up, but all in all it wasnt that hard and I know it will hold no problem.
But obviously, welding in a new piece of sheet metal is the ultimate fix.
thanks for the help 
i’m tackling mine this weekend 
yea mine are pretty bad as well… one of many problem spots on my car haha. i figure im jus gonna cut off all the rust n clean up whats left then jus weld in some new metal… easy enough