I am currently building a Sig Hog Bipe and have joined multi-color ultracote panels for both the fuse and the wings. I have used the technique of joining with over glass using my sealing iron.

At first I did the work directly on the glass, but found that a hotter-than-normal iron was required; I guess that the glass sucked too much heat out of the iron at normal temperature. With the higher temperature the joints were solid. I have since done the joins on the glass, but have placed the seem over a 1/4" x 1/2" balsa stick (to provide some insulation from glass) and find that this works better. I also cleaned the non-glue side of the film with alcohol before sealing.

I've not flown the plane yet, so I cannot attest for certain to the airworthiness of the joints. By inspection, however, they appear completely sealed and strong and I have confidence that they will survive flight.

With patience and careful execution I found this technique works well.