Split the area that can be leaking in half, use hose to soak one half at a time checking for leak. Once you find the half that leaks
it in half and repeat. Pretty soon it becomes clear where the leak is located.
I actually start out with four sections, bottom left, top left, bottom right, top right. Check the lower quarters first, then the upper. Also use a watering can with a sprinkler head. Makes it easier to direct water in a single location. Hose works too but is harder to just put water in a single small area.
Don't forget water migrates once it gets behind the insulation. Can move left or right (whatever direction is down) but always going down. Had a belly seam leak that showed up on the floor 3 feet away because that end of the trailer was lower.
Only time and persistence required to fix, but sometimes a lot of it. Good luck!