We had 30" wide bunks in our trailer when I was growing up. Fine in elementary school, okay in middle school, too small to be very comfortable by early high school. I usually slept in a tent rather than in the trailer at that point if we were going to be somewhere more than one night. At 28" I imagine that progression would be about the same but just a year or two earlier.
As for temperature, there was no A/C on that trailer, but it did have ~3' wide multi-panel windows in both bunks so if there was a breeze it wasn't bad. On a still and humid night that didn't drop out of the 80's it was pretty sweltering (not that a tent or the other beds in the trailer were a whole lot better).
Electrical outlets weren't an issue back then (limited personal electronics), and we do have outlets in our current trailer's bunks but I'm not sure it really matters. At home the kids charging points are across their rooms from their beds and it doesn't seem to pose a problem.