northstar
Hi,
I'm building one for a friend. I built up a keel by using a half inch square stick along the mid line of the hull. I then used 3/32 balsa to sheet it to the outer edge. This made a boat hull with a small keel. Before I sheeted the keel I used a 3/4 forstner bit to put about 15 holes in the bottom of the hull. After sheeting I used expanding foam to fill the void. In addition I painted epoxy & alcohol inside the entire hull. I also used goop around the pushrod tubes.
I think that good overlaps on the covering & not installing landing gear will go a long way in keeping dry. We will see
Ps. I built the keel to support the weight of the fuel tank that I mounted where the servos were supposed to go. I moved the servos up to the next forward area. Should limit the amount of weight I will need.
I never understood the tank in the rear. When you first take off your plane will be severely tail heavy. The only accommodations I had to make were to build a cradle for the tank, add really long fuel lines & install a perry pump.