yeah only need a little water and it will go rusty, you can get it filled with petrol and that will stop it and sticking the stablizer in will absorb any water that in there, you can get fuel system treatment that helps clean everything but keep the fuel system mositure free as well so mabye try that.

And you dont need a new tank, you can seal the tank you got with special sealant stuff, try frost auto restorers as i know they do it. the stuff they sell is made by the por 15 guys so it will be good