I built a teardrop trailer ( https://www.instructables.com/id/Teardrop-Trailer/... not mine but to give the idea) in 2011, this year my wife and I camped in it for a couple nights for our anniversary. While the trailer was great and allowed us to sleep peacefully and dry through 1" of rain dropped by a thunderstorm (try that in a tent) I still had to bring our changing tent as we didn't have a place to stand up for changing. Thanks to camping mid week we didn't have any real close neighbors at the campground, so the short step from the trailer door to the changing tent was no big deal, but if the spaces around us had been full, getting to the changing tent would have been a pain.
I had this idea in my mind but didn't have time to construct it before our trip, from now on we will both have a changing room outside our doors. if the weather is rainy I figure a golf umbrella over the ring would keep us dry.
4/15 Since this I'ble was written we have gone on many trips, the side tents are great! they almost double the private space of the tear, allow us to sit in the open door and get changed, just like the bed at home. We also use them as a potty tent, and have showered inside them as well.
here is what I used to make one side
10 foot 3/4" EMT electrical metal conduit
drill and bits
two ring-less cloth shower curtains, any shower curtain will work, but the ringless give privacy even above the hanger rod, a regular shower curtain hangs an inch or two below the rod. shower curtains were chosen as they are meant to get wet without trouble and are designed to give privacy.
flat aluminum stock
two stainless bow eyes (big U-bolts for attaching the bow rope to a boat) I got mine at Lowe's, a steel U bolt would work also but could leave rust stains, my bow eyes are rated for 6,000 lbs each, I should be able to lift the trailer by them!
a heavy rubber floor or welcome mat to stand on, something that will allow water and dirt to fall through easily . My store bought shower-tent floor tends to pool the water even with "drains' in it, a thick rubber mat with plenty of holes is more comfortable to stand on and dries quickly.