Battery Box Rusting - Best way to replace?
 

So I was wanting to freshen up my battery box, but after pulling up all the aluminum sheet on top I discovered substantial rust underneath. I ended up tearing out some of the plastic that was situation more toward the nose, so now I have a fantastic hole!

Whats the best way to go about putting in a new panel (cut and weld seems the obvious choice) and how much material do I tear out at the sides (plastic linings, etc) to get it clean for the install? Theres just a bunch of decaying plastic and fibrous synthetic sheet that seems like it needs to go, but maybe I was wrong for starting to tear that out.

Here's what I did - used a donor from a 944 Turbo (or any other 944/924s) and had it welded in place. Spot welds were drilled open to get the parts you need. Prepare yourself to remove the dash, the A/C stuff underneath as well as the carpet on the passenger side. Lot of work and that's really the only option I would consider to maintain originality. Later 944 battery trays have the additional water drain to the side and if you manage to get a turbo tray it will go faster, too...:)

A couple pieces of fiberglass sheets and some resin will also do the trick

Forgive me but that is some poor advice. Do it right or don't do it at all!

That method has been used thousands of times to repair battery boxes on these cars, there were even "repair kits" that companies sold with instructions and the right amount of fiberglass to repair the box. The best par is that the fiberglass will not rust out. I guess it comes down to personal preference more than anything

Thousands of times? Really?? Never
seen such a repair. Propose this method to a reputably body/restore business and they laugh at you. What you are claiming is just wrong, causes more damage down the road and simply destroys the value of the vehicle. The 924s eventually will increase in value but not with such a poorly executed repair. Best!