Of course the most used tool is a tape measure and pencil For me it was a low cost HF 1/4 router then a saber saw and a palm sander. Foamie's don't need a lot of power tools.
Cheap Electric Brad Nailer The one tool I did not know I needed was a cheap electric brad nailer I borrowed from a friend. This tool was very helpful securing the thin ceiling and roof plywood to the ribs until the glue set up. I used it on the hatch construction as well. Anywhere I needed to hold that thin ply to a stiffening rib, I grabbed the brad nailer and quickly shot some tiny nails until the glue took hold.
I bought 110 feet by 6 feet wide roll of frp. I did roof, floor, inside walls, and out side walls of my 5' X 10" drop. My favorite tool was an electric shear to cut the frp. It was Awesome. My Kreg jig was amazing too. Larry