We are forced to use an ethanol/ gasoline blend (E-10) in California. My fishing boat has fiberglass tanks.

While I see that you do not recommend your product for this application I am writing to ask if their is any history of success or another product you make that would be suitable for sealing fiberglass fuel tanks against ethanol blends of gasoline?

The Tank Sealer will withstand E85 and E10. That is no problem at all and Tank Sealer is used all of the time to seal fiberglass tanks using one of the convenient Tank Sealer Kits.

Please review the complete directions for Tank Sealer.

The section entitled "Fiberglass Tanks" reads as follows:

The procedure for sealing a Fiberglass Tank is the same except for a variance in Step #2 - RustBlast. For this type of tank, thoroughly wet the fiberglass surface for only 2 minutes using RustBlast. Drain and rinse well with water as directed. Because you are not prepping metal or dissolving rust, RustBlast may be saved and re-used for future use. RustBlast will, however, treat the fiberglass surface by giving it a more acidic pH level & by leaving a zinc phosphate coating ideal for Sealer adhesion.

Also, it is important to make sure that the tank is completely dry inside before sealing. Drying is best accomplished by introducing forced air into the tank by using a shop vac, blow dryer, or fan. (NOTE: Drying is a critical step for sealing fiberglass tanks. Fiberglass tends to hold moisture and if the tank is not dried completely, the Sealer will not adhere properly.)

IMPORTANT: It is also very critical to methodically coat the entire fiberglass tank completely & thoroughly with the Sealer. If any part of the fiberglass surface should accidentally be left exposed or unsealed, however, these unprotected areas will be very susceptible to deterioration by alcohol blended fuels and it is therefore highly recommended that these fuels not be used in fiberglass tanks even after sealing. After coating the tank, remember to drain well to avoid pooling and puddles.

Please let us know if that helps and if you have any additional questions about sealing up your fiberglass tanks.