OK folks, I took your inputs and came up with a simple tool that actually works great ! I mark the balsa trailing edge as usual, then I use two aluminum L bars on top and bottom of the wing. The edge of the bar is aligned with the pencil marking. The L bar provides sufficient in-plane rigidity to prevent deformation during sanding. I attach them to the sheeting by first applying a 1" strip of masking tape, then I overlay a thin 1" double sided tape onto the masking tape, followed by the L bar. Don't stick the double sided tape directly onto the balsa or it might damage it while removing the L-bar. The L-bar can be slowly remove and you'll find that the double-sided tape will follow it. Peel off the masking tape slowly in the balsa grain direction (it's harder to pull it off in the opposite direction). Once the top and bottom L bars are in place, just sand away with a sanding bar until the edges of the L bars are reached. I tried this out today on two wing panels and it was quite successful and takes out the chore from trailing edge sanding. Very precise, consistent and easy to do !! I guess the same tool can be used for sanding bevels in the control surfaces as well. Will give it a try next.