Fiberglass Bow Tank  BTW, note the picture with the 2-3 pounds of metal-rust-crud that I removed at first!!

I cut out the holes with a Dremel saw (or grinder) and saws-all (I can't remember exactly what I used).  This, after making sure the tank is completely clean and aired out. I filled the tank mostly with water to eliminate most of the fumes.  Then I cleaned it thoroughly with Acetone, etc and lined it with quality epoxy and roving (make sure to fillet all edges).  Next I created sheets of epoxy and cut out oversized covers with about 1-1/2". overlap.  I glassed these in with thickened epoxy on the edges and pulled up with elastic bands to spread the thickened epoxy and hold the bond tight.  Later, I reinforced the edges with a few layers of fiberglass tape.  You can stand on the access panels if you need to.

The original access panel is still removable to get into the tank for regular inspection.  If I ever needed to get into the other compartments, I could easily cut out and then regales the fiberglass panels, but I don't think there will be a need for that. 

Aesthetically and functionally it turned out very well. 

Chuck, T37 Mowe
chuckheb@mac.com