Acccording to the GW web site, they don't use fiberglass tanks. Here the Q&A where they say it. See the last paragraph.
Gary 89 Overnighter
Can I use 10% Ethanol Fuel in my Grady-White boat?
Recently there has been a great deal of interest in E10 Ethanol fuel or RFG Reformulated Gasoline. The use of this blended gasoline is growing. RFG is gasoline mixed with up to 10% grain alcohol or ethanol. This type of fuel burns hotter and cleaner which is better for the environment and makes us less dependent on foreign oil. There are some things you need to be aware of if you use these types of fuel:
If possible, it is best not to mix older type MTBE or non-ethanol fuel with ethanol fuel. In some locations E85 fuel has become available. Current outboard engines are not compatible with E85 fuel and it should not be used.
Ethanol acts as a solvent and causes any water, dirt debris or sludge build-up in your fuel tank to mix with gas. If any of these items enter into your fuel system from the gas tank, it could clog filters quickly and even get into your engine. We recommend installing new fuel filters before changing to ethanol fuel. 10 micron fuel filters have been developed by many outboard engine manufacturers to aid in the filtration process. When using RFG, it is more important than ever to check the fuel filters as part of your routine maintenance and replace them when necessary. Prepare ahead and have a couple of fuel filters on board. Lastly, RFG has a shorter shelf life compared to normal gasoline. It important to add non alcohol fuel stabilizers with every tank of fresh fuel.
For long term storage and winterization, Grady-White recommends storing your boat with a full tank of fuel. This will reduce the amount of water vapor in the tank and therefore reduce the amount of water in the fuel. Be careful not to over fill the tank, this could cause fuel spillage through the deck air vent as temperatures increase in the spring.
Recently, there have been reports in the media about ethanol fuel damaging fiberglass fuel tanks. This situation does not apply to Grady-White Boats; we have never used fiberglass fuel tanks. In addition, all Grady-White fuel system components (hoses, fittings) are compatible with E10 ethanol fuel.