All these ideas are great but a problem Im seeing is that CA has already been used on the area. Once you use CA or most other glues, nothing else will stick to it, it has sealed the wood and CA is the hardest to get off.
If posible, replace the wood in that area and start over. I have very good results applying thinned epoxy to the covering edge to seal it to the balsa and then paint the firewall. Try to use CA as a last resort for covering repaires.