Teardrops n Tiny Travel Trailers

And then you need to leave a window open to avoid oxygen depravation.

Just remember that you can get very close tolerances when the teardrop is not moving. But once you put that teardrop in motion and things start moving around a little, tight clearances may open up. Another dynamic against tight clearances is thermal contraction/expansion. Lastly, if your door has any thickness at all, you'll have to leave tolerances for the door to open - the door "lengthens" on its swing - and/or bevel the door to clear the jamb.

'Throwing out a couple ideas here:

1 - Mount a vent fan at the top of a sidewall
where it meets the ceiling. Often used in
early house trailers for cook-stove exhausting.
Hinge the cover at the top and it is usable in
the rain too. As an example, Wolfscout added one
to his CT conversion.
See the 4-4-12 post on pg 9 of his CT build thread:

viewtopic.php?f=42&t=44867&start=120

2 - A fast easy way to accomplish what you want to do with the door,
would be to make your door larger than your opening by an inch
or a little more the entire perimeter of the opening. This will overlay
on the outside of the opening and bear against the exterior sidewall.
A nice wider and/or thicker compression seal would be mounted adjacent
to the outer edge of the interior facing side of the nominally oversized door,
or against the corresponding sidewall opening perimeter.
Then use/apply a perimeter trim/frame on the exterior wall of the same
thickness as the door's thickness around the door mounted with the desired
perimeter clearance. Hinge type/mounting would depend on your preference.
Beveling or rounding over the outside edge of the trim/frame around the door
would be a nice touch as well. This is a simpler more straight-forward method
that results in almost a refrigerator door style seal. It avoids a lot of the angst
involved with trying to fit your door into the opening shape and plane, especially if
one hasn't taken the pains to cut out the door opening with the thought
of using the cut-out as the exterior door skin. Remember to use the appropriate
caulking and sealing and wood sealing.

Just suggestions for consideration.

Cheers,
Norm/mezmo

Wood which likes to expand and contract with the humidity, may be an issue. Your nice fitting tight door may end up being a stuck door given the right environmental conditions.

It seems like many people try to make openings in their teardrop water tight thinking that a car is water tight. Well a car is not water tight, they just redirect the water around any openings in a car. There are run channels and drain tubes to move the water from coming inside. It is far easier to redirect water than stop it. Just my thoughts.
Brwbier

You may also run into a problem with the doors not wanting to close due to air pressure. As the door closes, if the air has no place to go, it will begin to compress, and the door will bounce off the compressing air and not latch properly