With all the hassle of removing and re-installing a tank, along with trying to purchase the correct tank, you might want to give a tank patch product a try.
I saw this product installed on a demo small holding tank at RV Trailer Parts Supply in El Cajon, California. I couldn't pry the patch loose from the tank with my fingers. RV Trailer Parts also does business as Specialty Recreation at the same location in El Cajon.
On Edit: BTW, the instructions on this patch tape call for Acetone (nail polish remover, unscented) surface prep.