On the front door, I used a Magic Mesh screen that costs $14 at Walmart or similar. The screen is a little too long, so I pulled off the top magnet and rolled it a couple of times around a 1x2 that is painted to match the trailer. The 1x2 is a little longer than the screen is wide, so I had room on the ends for a screw. I stapled the Magic Mesh on the sides about 2/3 down so it was easier to go in and out. When the first one needs replacing, I will probably bunch it up just a little to provide some room up top as well. Has worked great for lots of days in the woods. This $14 screen works exactly as described, go through the middle and the magnets automatically close the screen behind you. The dog figured it out the first time in and out. Here is a picture

Since I wanted flow through ventilation without the bugs, I had a screen made for $70 for the rear and attached with Velcro on the top and sides. Here is a picture. Sorry, trailer was a mess when I snapped the pictures, as we had just gotten out of bed and opened the trailer to enjoy the sun while Sandy got ready for the day and made breakfast. Once we arrive at the camp location, we pull the motorcycle out of the trailer, fold down the bed and install the screen. The screen stays in place until it's time to go home, as the rear doors will close without touching the screen. On hot evenings, we leave the doors open and just sleep with the screen in place.

The rear screen is super easy to install, and with the Magic Mesh, we have full screen protection from bugs with a completely open trailer. Here's the link for the company that made the screen.
http://toyhaulerscreens.com/onlineorder.htmlThe rear screen is very high quality, and should last a long time.
Rick