Joe, What I have been doing on profile models is use 3/8" balsa, for the fuse, installing the motor mounts to match the engine of choice, cutting out behind the flaps to the l/e of the stab, then put in diagonal (30 degree angle) braces of 3/32" balsa, they are 3/8"wide, cover each side from nose to tail with 1/64" plywood using 2 hr epoxy, in a very thin coat, to adhere the plywood to the sides.
I usually do one side at the time and I put the fuse on a flat surface between two pieces of 36" or what ever needed plate glass and let cure over night, then do the other side the same way.
I can't take the credit for this method as Tom Farmer enlightened me to this several years ago, you will add about one once of weight, but the strength far outweighs the weight gain.
If the two hour epoxy sets up too quick then by all means use a slower curing type...
Hope that this helps,