Your might be different than mine but mine fits over the lip and attaches that way. Easy to take off and put back on if needed. If it is coming apart look to see if glue would work. As for testing it, if you turn the light on or put a flashlight in there at night and close the door you will see where potential leaks will be. Also I sprayed mine but did not have to go inside, not that I would fit, but I just looked from the other side of the trailer. Once you open the door you will see if it leaked and from where. Good luck.
