Depending on how aesthetically pleasing you want I'm aware of aftermarket aluminum sleeves made for plastic fuel and oil tanks of power sports equipment, snowmobiles etc (particularly Arctic scrap) sorry cat fans lol. Depending how handy you are could probably make your own steel or aluminum sleeve with a collar fastening to top of tank with mechanical fasteners and solvent resistant sealant. Imo and experience doing this to plastic fuel tanks it worked for me and is a cheap backwoods hack. Apologize for no pics.