Next time you empty tank use a little MEK (Methyl Ethyl Ketone) and melt down a little plastic shavings and fill scratches (after cleaning them very well as anything left in the scratches will always remain there after you fill the scratches). What you are doing is basically the same as welding your seams. Your just using a little extra plastic as filler. You will need to use a syringe (or squirt bottle) and needle just as you would with new seams. It will be self leveling, and you are better filling in several layers than you are to over fill and then have to remove excess by sanding, then having to buff or heat melt the scuffs out. You can get little 6 to 8 ounces bottles at hardware stores where they sell their Plexiglas, along with a little squeeze bottle and a needle, or you can go to the solvent section among st the paint and buy a one quart can of MEK for just a little bit more. Syringes and needles can come from hobby shops or a pharmavy or where ever. I personally get mine as needed from my doctor. Mek, with lid screwed tightly, has a shelf life as long as the can will go without rusting through. A long, long time.