Is your water tank mounted underneath the trailer floor, hanging down onto support rails?
If so it's possible that the bottom of the tank is sagging between the supports and the pump intake ends up above the pools formed.
Again, if this is your setup, adding support (like plywood) under the tank that holds it's bottom flat will alleviate the problem.
If your tank is mounted in a compartment, above the floor (as it was in my old trailer) you might have to relocate the pump inlet. Install a glue on flange on top of the tank then create a suction tube that will extend to the bottom of the tank, extending through a compression fitting. Cut the end of the tube at a 45 degree angle so it doesn't seal itself off at the bottom of the tank. PEX works great but I've seen this done on boats using stiff polyethelene tubing. Water is sucked out of the tank just like fluids are sucked up from spray bottles.
One question, are you running out of water while the gauge still shows you should have water? If so, then you definitely need to relocate or revise the water suction "port".
"A wise man can change his mind. A fool never will."
"Sometimes you're the dog, sometimes you're the tree"
2018 Flagstaff Micro Lite 25BDS
2004 Nissan Titan