Here's my solution
I have screens for the side and end of my shell. A shell can warm up pretty fast but with these screens, the shell works great. I had them made of heavy duty screening material that can be had from a hardware store or upholstery supply or go the an upholstery shop and have them make it. I did the latter as I don't have the skills or equipment to do it. The covers snap on to snaps that are screwed into the shell. At least here in the southwest, I have found that velcro that is glued to something does not hold up and it will eventually come off. I had a tent trailer for a while and had to redo all the parts that were velcro.
Here is a pic of how the screens look.
Here is a shot of how I boxed the area around the lift bracket.
Though I do not have a picture of the back cover, it is the same but for the bottom. It snaps on to the shell on the top and sides and then I use a few magnets that I got at the hardware store to connect the cover to the tailgate. I did not want snaps on the inside of the tailgate (or anywhere on the tailgate for that matter. I have no doubt that the snaps would work as well with a fiberglass shell as with my metal one and if you do not have anywhere to mount snaps on the bottom, you could use the magnet idea as I do on the back. Also the covers roll up when not in use and take up very little space.
With the covers snapped on, I can comfortably lay in bed and read, play cards etc with as many lights on as I want and not have any issue with bugs and the shell stays as cool as the outside temp.
Mikey