They had something like a 2 inch strip of thin inslation in the two recessed areas on the top of the tank. I think directly above the strap location on the bottom. You should be able to use just about anything on it.
Also be careful on the first fill up, I know some of the aftermarket tanks they put the filler neck to far into the tank so when you go and fill it up gas will start running out of the neck at half full leaving a big mess on you and your ride.
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