http://www.autozone.com/autozone/accessories/Miscellaneous-Non-Automotive-Products/Marine-Fuse-and-Accessories/_/N-2753?filterByKeyWord=fuse+holder&fromString=search Any local auto parts store should have at least a few different types in stock... This is certainly the ideal method, use a relay to make a dedicated switched circuit, that way you have convenience AND proper circuit protection. you still run the risk of losing your circuit that you're tapping for the relay if the relay get's compromised, or you don't properly seal for water ingress, but the GPS and phone might not be drawing much more than the relay, making the relay less beneficial. If it were a higher draw device, like extra horns or lights, or heated gear, i would definitely suggest another circuit, but for a couple amps... might not be worthwhile.