Yes you are on the right track make a window to see inside then glue it back in place with a layer of glass over it. Pound around to make sure you don't cut into bulkheads. Make the cut on the inside face of the hull not as bad to fix if you aren't good at faring and blending or want to rush. Use west system or other epoxies and don't use auto body filler it will pop with time. Ask the builder for their advise. You may have to make several windows and make them big enought to work through.