How did this work out using gravel? We are currently attempting to build a cool room. We have the panels, just talked to calf cooler and they said the refrigeration would be $18,000... Of course I laughed wildly , thinking cool bot only cost 300-400. Even if I had to run 3 24,000 BTU A/C's brand new worst case $3,000 for refrigeration. Am I wrong in that assumption? We will range from 4 calf's to 8... Depending on the time of year. We really only need to reach a comfortable temperature 65-70 degrees inside the room, as the calves will be going to shows in 100 degree plus heat for fairs and Arkansas youth expo. Last thing we need is a calf having a heat stroke walking out of a 45 degree cooler in 111 degree heat. .. please advise if my thinking is wrong..