Hi madmuz. The rubber patches are at the ends of the tank. Two at one end and one at the other where the tank meets the brackets and chassis respectively. The attached photo(not my tank) and diagram will give an indication. I did see a Youtube video where rubber was also placed under the horizontal straps to stop rubbing. I did not think that this was a good idea as the tank could potentially move out sideways once the rubber compresses or decomposes as the tank grooves are shallow. You make a good point in regard to earthing the tank and subsequently the sender unit. With both the straps and tank painted, it will be electrically isolated. I will make an earth strap for the tank. I left the sender fittings unpainted.