Hey, David H --- Question about Rear Shock tower pads.

Clancy, the only real experience I have had with these is replacing them  in conjunction with remounting the body which was off the frame.

You may be able to separate the body from the mount by the shocks without loosening any other bolts but the other pad goes through one of the bolts under the rear seat and you'll almost certainly have to undo all of those, and possibly a couple of the rear pan bolts.

I wouldn't worry much about disturbing the body to pan seal.  I've not known these to tear unless they're 50 years old.  As far as leaving a gap in the seal when putting in thicker pads, tightening the bolts all the way around sucks up any gap you might think you've made.  If it's a concern, use some flexible silicone seal or something similar. 

As far as modern rubber not holding up, maybe you could go with a slightly thicker pad than you need and overtightening to the thickness you need.  This may not be a good idea since you'd be hardening the pad and defeating it's purpose.  These pads aren't high tech, you might be able to find something similar at Advance Auto of Pep Poys that are of a longer lasting compound.  Of course it would be a few years before you'd know for sure.

David

Clancy, I don't think you'll have any problem. I've replaced them in early cars before just by undoing a few of the bolts under the back seat and never actually broke the seal.
I've been recently messing around with one of my Mexican beetles ( 2004 body - 1965 chassis) because the '65 chassis mount at that point is lower than the 2004 body I've been working on diferrent spacers and think I have finally come up with a winner using a motor mount bolt two large washers and a cut down rear rubber suspension snubber.