Have a camper, trl, 8'x 20'pull type. Water has come in around the A/C on top and let the water come to the inside ceiling and left a big brown water stain on about a 2 1/2 x 3' section. Put caulking around the a/c and then put Kool Seal on the entire roof. What is the best way to handle the water stain? I put a primer over it to cover it up. I bought spackling and flat latex paint to cover the entire ceiling.