I agree with Vince about 3M-77 ,a lots of problem with this product the skin on my Zero started separating after a year. On the next plane I used Southern's Sorghum with great results here is link to give you some idea's
http://www.eam.net/DBROWN/bldsupplies.htm
If you decide to use S. sorghum make sure to seal the inside part of the skin with Balsarite or equivalent first otherwise a lots of sorghum will be absorbed by balsa.
the only disadvantage of sorghum is once the skin touches the core it is an instant bond and there is no moving around so measure and plan ahead. Good product. Next I have also used epoxy and it worked OK but the it is heavier than all methods