I've been out remeasuring and thinking...... I might just go to a light 3/8 just to be safe. My first attempt and this part is harder than I imagined it to be. This isn't a regular Teardrop, but more of a utility type trailer that I initially wanted to install some 4x8 walls on to make it more stackable for a road trip.... then I went a little crazy and started enclosing it. Next thing I knew I had opened up the roof ( that wasn't suppose to be there) for a roof vent.... and on it goes. Having fun and learning alot of things for the first real Teardrop I build. My dog has already staked out this trailer as his own doghouse....

In it as we speak snoring away.
Anyway, back to the door.... what magic words should I search on to bring up the inner or outer seal system you mentioned? My searches tend to turn up several thousand hits and very little to do with my search intentions.
The trailer has 1/2 walls out of cheap 4 ply junk plywood I got for about $12 each. Remember it was going to be just some sidewalls when I got started..... WHEW!! I finally got them straight enough and have put the door framework at the rear. The trailer is 5x8.