Good question and I use the same technique as giant scale planes. That is to position the fuselage straight up and down on the board and use some weight to hold it down flat. Make sure the sides are vertical by using a square on the sides. Once you are satisfied with this then glue the vertical stab in place using what ever glue you like. I just use thick or medium CA. While gluing use another square to make sure the stab is perfectly vertical. Also make a mark in thecenter of the fuse on the top where the front of the stab positions. this will assure you keep it straight as well. Center the fin post on the back and glue with CA as well. Hope this helps.