Sunfire,

a 55 gallon barrel is equal to 7.35 cubic feet of water. The area of the top of your barrel approximately 2.125 square feet and the height of barrel about 3.45 ft tall. The area needed to fill the 7.35 cf in a 1" rain is approximately 90 square feet. You could build a 9' x 10' tent structure that funneled into you drum. A 4.5' x 5' tent would fill your drum in a 2-inch rain. How many storms do you get in a short period of time? You realize the most pressure you can get for a barrel sitting on the ground is about 1.5 psi with the tank full. Aloha