I am scratch building a little sport plane of RCM plans and I can't figure this out. The plans call for a wing bolt filler block to be positioned at the trailing edge. I understand its function. However, the plan does not specify what material I should use. The actual wing bolt block in the fuselage will be plywood. Will 3/16" balsa sheet suffice for the filler block, or does it also need to be plywood.

Thanks