I know, body work sucks but the GPW that I just picked up to restore has about as many holes in the tub as swiss cheese..

I have heard about the copper plate method of filling holes, but how thick does it have to be? Or is there a better way?

This is going to be a low buck restification so buying a new tub for ~2K is not an option..

Anyone?

I don't use "the old copper trick"so I don't know.
I'd just buy some sheet metal and cut-out some patches, tack it over the holes and cut thru both pieces with a thin cut-off wheel. Then spot-weld the new (perfectly sized) metal into place, grind and fill.
You will need to shrink the metal to get it flat again...Find a high or low area, heat a quarter size spot red hot, back it up with some heavy steel and smack it with a hammer, then cool it with water. It will take some work, but it will straighten out if you work it enough.

Kill the rust and fiberglass the back side and fill the holes. Copper is used as a weld stop if you use a mig to fill in the holes with weld. The copper is not left behind, and a thin sheet will do just fine.

The last time I did it I used 16 ga. copper, that is what I had laying around. The copper is just a backing, the weld will not stick to it.:D

Depending on how bad the rust is the best and most effective method would be to cut out the rust and replace the cutouts with sheet metal patch panels...If done properly you will not be able to see the repairs. It will last much longer than glass....
I tried glass, but it is very tricky to work with, and it will crack while wheelin (body flex).
One other thing, body work sucks....Almost as bad as exhausts!!:skull:

I knew that the copper plate would not stick to the weld but I thought that a thin piece of copper would melt...:confused:

Guess not..

COOL!!
thin copper is cheap :)