Lining a new or used gas fuel tank is a good idea. The fuel nowaday contains parts which in longer therm, which means standing at home, after some times will change to esters, which is a kind of acid and starts to eat sheet metall. The result is brown looking gas. It is just a matter of time until the new tank is scrap again.
All my gas veterans have lined tanks. I do not make it myself, even it costs a little more. So far I have no real good idea to tumble the tank for 24 hours that the solvent of the liner realy covers all parts.
Wolf from Germany