OK, you muddle through somehow. Oh - yes. Step three - fill the troughs with sand. Have a dude in a bobcat loading sand in, but keep it out of the guns, thank you. Pack the sand, by hand.
Gloves are nice, at first.
But as they get wet, and caked with sand, you wonder. Racks are sets of guns. OK, image a pallet - one of those wood thingies at the bottom of a 6 foot stack of toilet paper at Costco. Stand it on end, and shove in some PVC pipe as mortars. That's part of a rack.