Mine has 2 openings through the side of the trailer - one for each tank. When PO removed the tank he made a plate to cover the hole and removed all the plumbing. He added the locking cover on the remaining fill opening. I got the tank when we bought it and reinstalled it. I like the one on ebay but would like to find one with a gasket like the one on the trailer.
I've been trying to figure out how to post a picture of the trailer in my profile but haven't got it yet. Will keep trying.
Thanks for the info.