putting up tent trailer door onto roof for travel

[shinobi]

Excuse me if this question has been answered somewhere else already. I just bought a used tent trailer. It's a 1979 Viking, and for its age and price, it was a great deal, but there are some things that need to be repaired. The roof has been repaired by the previous owner and the outside is finished, but the inside ceiling is bare styrofoam and the latches to hold the door are missing. Well, I have the latches I believe on hand, but they aren't installed and I'm not sure how to install them. Will I have to remove the top aluminum to install these latches or is there a better way?

Any other advice on this issue would be welcome.

Thanks