I purchased a Fuel tank pad from Flyboys Accessories (their add is on this site) and put it under my tank. Now as you know the clearance under the tank gets larger from the back baggage wall to the center structure. So I positioned this pad where it would make good contact with bottom of the tank, but not push the back up to much.
Where those flush screws are, and any other spots where any contact between floor and tank appear in the bottom back, I use some heavy anti chaff tape. This tape is one inch wide and has a peel off backing to expose the sticky side. As I recall after the first year I removed the tank and noted a few spots in the back area that left coresponding scuff on the tank bottom. This was four years ago now and no issues with the tape barrier.
Also the Fuel tank pad has a peel off side to be able stick it down. Not being sure if I would continue to use it, and where I would place it, I never stuck it down. I would say it ended up between the baffle and back of the tank.
Arvada, CO BJC
RV12, #401, Flying 2013, N612PC
RV6, 1996-2010 sold