My RV style roof mounted AC unit committed suicide and I just spent 3 grueling days installing Central Air and Heat in my older Allied 39 Ketch. Actually only 2 days of really physical labor and 1 full day of thinking it out. It initially looked like it would be a piece of cake. Yeah, right!! I should have known better. Anyway, with all tools in hand, it turns out that the most used tool to make my cut-outs, believe it or not, was the Dremmel. After many trials and errors, I think the whole job could have been done with just a Dremmel and an electric drill. Thought I would just pass that on. Tony B