The balsa will get soft and weak if you do not protect it from glo fuel ,even with no nitro in it
That will shorten the airframes life span
The issue i think is the oil soaling into th wood ,as the alcohol and nitro evaporate ,but the oil does not
i have been working with glo fuel for a total of 30 years , in control line and then RC for about 25 years
I fly only two cycle glo
If you have any interest in two cycle ,you might like to see my notes on the subject
Forums --RC Airplanes --Tips and techniques -- what you have learned to keep your glo ( two cycle only ) aircraft flying more reliably
Rustoleum hiigh gloss ,white and black are both fuel proof
My first choice , to fuel proof is , Sig buyterate clear dope ,very light ,and dries super fast ,but i am old school with my building techniques
You can seal your seams and decals edges , from your fllm coverings ,so hot fuel oil does not work its way under a film covering by using the Sig dope ,paint over the seams
You often cannot see that it has been applied to a film covering ,so its a win win ,to keep the airframe sound for many years
A number of my planes ,i have been flying for 20 years
You can see my --Gallery --to the left of this post , for some of the best flying two cycle glo aircraft , that have been available for the last 20-25 years
Enjoy !