Just removed my propane cover and tanks for inspection and find that both tanks sit in about 1/2" water trapped by the propane tank holder. Drilled 2-3 holes in each side to drain water and keep it dry.
Jim never in doubt, often wrong
Jim.. to add to your thread I've also observed on my 19 that the metal screws securing the propane tank tray to the trailer frame that are only visible when you remove the tanks for filling, were loose, and in one case stripped
Jim ,just a point of information . If you drill a small round hole with a drill bit ,often the water will skim over the hole due to surface tension and not drain or drain poorly . It is best to elongate the hole to facilitate draining . If you look at the factory drain holes in electrical equipment such as a meter socket the holes are triangular or slotted.to improve drainage
My Casita did the same thing in the area directly under the tank