Dave, the fin will be a nomex honeycomb core with 1/16 balsa sheeting, the rudder will be built up balsa. Wings and stab will be sheeted foam. Wing airfoil is one that I designed a couple years ago and is working well on other models. The pipe tunnel is a simple sub floor just below the wing tube. Access will be through the top via removeable canopy from the back edge of the cowl to the turtle deck. The cowl mold came from an old Rogas Modell Dalotel kit. It came with a plastic cowl that I used as a plug to make the mold so I could lay up a glass cowl for that airplane.