What size wire feeds it? That pump should not be blowing a 30 amp fuse any way any how. Run at least 14 gauge wire from a good source of power to the hot side of the pump (blue wire) and make sure you have a good ground. It is a good idea to run a ground to the front of the car and bring all of your grounds to it. Does the wire get hot before it blows the fuse?
you would be shocked how much amp draw capacity drops off when an auto-reset type breaker gets warm from ambient temps. also in-rush (when motor turns on) needs from the pump motor can be way beyond the given rating of the relay, even before it warms up and becomes less capable.
you said popping the relay, did you mean the breaker ?