Sorry...late to the confusion....As far as I know, not all even polyester tanks are damaged by ethanol gasoline...it was certain types used through some years of boat building. It may not be recommended in a general way...but checking with the manufacturer is best as there are plenty of underground fiberglass gasoline tanks that I bet may not be exactly the epoxy we are discussing. There are many, many formulations.
This thread is a great example of do your own thorough research.
Here is some gas and diesel and ethanol resistant epoxy you can buy on Amazon....
Gasoline Resistant Epoxy- MAX GRE Resin for Coating, Bonding, Potting, Fiberglassing Reinforcement & Repair - Resistant to E85 Gasoline & Diesel Fuel
https://www.amazon.com/Gasoline-Res...asoline+resistant+epoxy&qid=1642438381&sr=8-3
As far as fittings go, I do believe ABYC suggests no fittings anywhere but on top. I have their older versions on a different computer.
https://newboatbuilders.com/docs/PY_JAN09_51-54_FUEL_TANKS.pdf
Fittings
Gasoline tanks may not have
openings below the top of the tank or incorporate tank drains or sight tubes, but diesel
tanks commonly do. Sight tubes should have
a valve at either end so they can be closed to
prevent leaks if the tube breaks. Diesel tanks
usually have a clean-out port on the top of
the tank. All fittings should be galvanically
compatible with the tank, so, for instance,
brass should never be used in contact with
aluminum. Steel or stainless steel is the
most common material for fittings. One
item that causes headaches is the tank
sender, which tells you how much fuel is in
the tank. In most tanks this is the old
resistive, float-on-an-arm type. The arm is
connected to a variable resistor. As the float
goes up and down the arm moves, the
resistance changes, and the level is indicated
on a gauge. Such senders, however, are
affected by motion and notoriously
inaccurate......
Also info from the same article.
......Tank Standards In the U.S. and Canada
the respective Coast Guards regulate fuel
tanks on recreational boats. U.S. standards
posit the absolute minimum for safety, so
most manufacturers follow the American
Boat and Yacht Council (ABYC) standards,
which are more comprehensive. In Canada
the standards are taken directly from ABYC.
ABYC is a non-profit organization that
employs volunteer committees of designers, builders, surveyors, government entities, boat owners and other interested parties
to determine, by consensus, the standards.
Groups such as the National Fire Protection
Association, the Society of Automotive Engineers and UL also publish standards. These
are incorporated into ABYC standards. If the
tank meets ABYC standards, it will also meet
the national standards.