There's always someone who will disagree and I guess that's me on this one. What Vinnie and Jack are recommending will work fine, but let me point out a couple of my thoughts; then you decide.

To merely fuelproof you only need to dope the area. If you're looking to strengthen the structure, the finishing exopy works somewhat because it tends to soak into the balsa as it cures. If the dope were applied first, the epoxy would have less tendency to soak into the grain.

I recommend epoxy first, dope second, mount engine third, and fly for fun fourth. (had to get that alliteration in)