I am not clear as to exactly what you are cutting but here goes. Take a long blade for a sawsall and I mean a 10"or longer lay the saw on its side and start the cut at the bottom of the piece of wood glass whatever the material.On the other side of the traveler where the blade will be running use a piece of mica to keep the blade from scuffing the surface of the cabin top or what ever the blade will ride on that mica and not the cabin top.If you bend the blade and apply a little pressure while cutting thats ok it will work for a few cuts and then youe job is done don''t cut real fast just smooth and a meadium speed.The trick is to keep that blade flat thats where the bend comes in and dont let the saw head bang into the cabin top.If you have to cut through SS bolts a metal blade should be used it will cut wood to but a bit slower. This method can be used to cut many differnt things on boats old stringers from the hull without damaging the hull, travler blocks ect.
How ''bout Dremel type rotary? full assortment of blades, grinders Etc, can use cable for tight spots. Takes a lot of patience (& blades) sometimes but can get into some tight areas ? Some compressed air grinders have a small handle for heavy jobs.