I would get and RV water pump that delivers somewhere around 2 gpm and wire it for how you are going to power it. I have a 12v water proof cigarette type plug on the utility side that is protected with a 10amp fuse, so that would be the deciding criteria, for me. I would probably spring for one of the larger bladder tanks that someone has mentioned. Yep, just shop around. With just a quick look I see a pump at HF that is claimed to pump 260 gph, which is probably bunk. But has clips and might last you all you need it to.
12 Volt Marine Utility Water Pump
If I did this alot, I would consider one of the better brands... shurflo or flojet.