On my '99 GT, there was a roof leak, and I found out that the mirror was only mounted to the filon and luan mahogany. The mounting screws had rusted almost out of existence. The mahogany had dry rotted in that area so badly that there was no chance of a replacement, even larger, screw holding!
I bit the bullet, drilled all the way through, and used a piece of teak about 2-1/2" X 4" and stainless bolts with acorn nuts on the inside. That worked quite well.
Oh, the leak was where the front cap met the roof.
2005 Georgetown 342DS XL, Full Banks Package
2005 Liberty Renegade 4X Toad
1989 Wrangler Sahara Toad
1984 19.5' Beachcraft i/o 5.o liter, 4-bbl (and you thought your Moho sucked gas!)
D/W Carole and Maggie the Teacup Lab (Black Chihuahua)