* It T-storms on every camping trip I've ever gone on, even when I was a Boy Scout, so I built my trailer to be reasonably rain-tight as a consequence. I used compression-type automotive doorseals, that I had leftover from restoring my old '69 Chevy C-10 pickup (I wish I still had it) in the late '90's. The seals are mounted on the 1/4" inner doorjambs of the oak bracing surrounding the solid 3/4" plywood doors (totally sealed with "the mix", and multiple coats of poly and paint), and the bottomside has an exterior doorsweep hanging down as a drip-edge, protecting the aluminum threshold there (no rubber seal there, just a wood/aluminum interface).

- doorseals and water protection.jpg (131.87 KiB) Viewed 2042 times
* I tested it with a garden hose on "jet-spray", and no leaks. I also made an rain deflector for each side, of 1.5" aluminum angle, to shield the front and top of each door from wind-driven rain (actually, for driving thru the rain), and sealed them to the trailer with PL adhesive, as well as with screws. They also work well, with no leaks. And, I cover my entire 4x8 squareback TTT with a 8x8 canopy, as well, at every campsite (I carry along a spare canopy, too).

- rain-proof camping set-ups I use.jpg (254.07 KiB) Viewed 2042 times
*
However, one must-do thing about sealing out water, if direct impingement upon any doorseal is possible (like happened to me before I stated using the sidewall or side tent to cover the secondary door), is to make sure that the door is
fully closed. During a monsoon-like day at camp, a few years back, I was away from my trailer all day, before I went back at nightfall. The secondary door was not fully shut, and thus the compression seal was ineffective against the heavy ran...and especially useless versus the canopy periodically dumping loads of water on the deflector just above the semi-open door. Needless to say, water got inside, lots of it.
* I usually tilt my trailer by 5 degrees or so, to keep any water from possibly pooling on the flat roof, and that angle made water that got in become 1-2" deep under /around my foam mattress (luckily sealed in a bag); but, the carpet was soaked, and after drying it out as well as I could, I spent a miserable night with my 11" fan on max, the A/C on full (to relieve humidity), two heaters (200 watts each) going, and my awning windows open. After that, I made sure that
- 1) my doors are fully closed,
- 2) I have plenty of towels in reserve (for water absorption),
- 3) my mattress is on 1.5" spacers above the floor, just in case,
- 4) I block the secondary door at all times with the sidewall or side tent,
- 5) re-check my trailer more frequently in heavy rain