How to seal these corners? Eternabond tape?

I recently tried the blower test. I did not find any leaks but was not impressed with this method. My camper has too many big leaks to make me confident about finding small ones. Big leaks included the Heki. There is no seal just a lip to prevent water from entering. The outside shower area also leaked. There is a big hole through the camper for the shower hoses. The door is just plastic without any seals. Water that enters just drains out but that system is another big leak that does not allow pressure to build in the camper.

I can also add that it is a waste of time to wax the camper and then test for leaks. The soap solution partially removed the wax and caused streaking. Afterwards I had to strip off all the recently applied wax and start over.