under seat fuel tank

I have used pieces cut out of an old treadmill belt for simular uses, it was cheap (free), kind of smooth on the underside and has the stipple type texture on the walking side. Pretty tough, fairly thin , doesnt absorb water and is electrically non-conductive.

 

Your problem sounds like the rubber strip. Pull that out and put a cheapy floor mat or something like that that has hardly any thickness under the tank or better yet, put some roll-on or spray on bedliner right underneath it just to keep the tank and tub from rubbing and causing rust.

 

I use rubber bungie cords with the fat ends cut off