If the fuselage uses polyester resin for the lay-up there is something you should know and this is why you can’t get a good bond to it. Polyester resin will not cure to 100 % unless it is in a vacuum or oxygen is removed. You can’t always put a large lay-up in a vacuum so they add styrene to the resin and what this does is float to the surface and form a film to keeps the oxygen out. Styrene is a wax and unless you remove it nothing will stick very well including epoxies designed to bond to polyester. Depending on who made the resin they could have used very little of a lot, so this will need to be removed before you can get a good bond to it. You may need to sand down to expose some of the cloth before the wax is removed. After you get all the styrene off any good epoxy will bond to it, Hysol works great , but I found that West System Six-10 epoxy works better.