Sorry to hear of your problems with the Hobby Lobby foamcore. I have been using all three thicknesses of this stuff and havent had trouble with it warping on me. I dont face the wing leading edges with the wood, I just use hard balsa for spars at the hingeline on the tailfeathers and lately have been useing those dowels at HL in the wood stuff area for spars in the wings. They come in several sizes and I glue them on to the bottom of undercamber wings and then put strapping tape over the dowel to kind-of smooth it out.
Have you found out this foam has a grain? It is several times stiffer bending one way then the other. Always run the stiffway, longways for all your parts like wings, fuse sides and horizontal stabs. Also I have found over the years that if you paint the top of a wing, paint the bottom also because the painted side will tend to draw it up, dont know why but it does....What kind of glue are you useing, maybe that is a problem, but I have used about all the water base glues out there and have been OK.

Maybe you just got a bad batch of foamboard, I have used HL and Dollar Store stuff for about 4-5 years, maybe 25-30 planes built. Fly em till the get rough looking and them hang them up of give them to the neighborhood kids to hang in their rooms......

Good Luck
Bob