I say go custom or just go find a couple of magnets (the rare earth have a good amount of gusto the 'em), dip them in plastidip, let them dry, give them a solid wash in the dishwasher and BAM! rust-proof, low-profile magnets that you can use on both sides of the tank and would basically look stock.
If you were in Van I'd machine a rack for ya for some frags
