That is where I mounted my relay, up in front of the battery where it's hidden. Works great! Make sure to use a fuse in the power lead to the relay, and use a big enough wire for the lenght and load. I'd bet you want at least a 12-14ga wire.Ok, but have no nearby power source have the battery mounted in front. So I´m going to mount the relay on front inner fender if you think it still will work with so long cable between relay and pump.
Another thing I did, was put an oil pressure switch inline as well. This will shut off the pump in the event of an accident or engine failure... If I got in a wreck, i didn't want it to continue to pump out gas.... I also run my ignition (on another relay) off this oil switch. I figure it will shut down the engine in the event of oil pressure loss, and may save me a few $$ in repairs later if something bad happens.