Mine was built us--AS I HAD TO CUT IT OPEN TO REPAIR THE AITI-ROTATION DOWLS--AND EMPTY SPACE INSIDE THE WINGS MEANS BUILT UP!!!! Of course since they are fully sheeted you would not know that unlewss you called Rocco or else had to do surgery--AS I DID!
I also just checked the website and it says nothing of foam cores-made of balsa and lite ply-you may want to look for your self. Here is the link
http://www.aero-works.net/store/detail.aspx?ID=81