I think you might be better off looking at the detached pop-up screen rooms — there are numerous ones on the market.
The problem with most add-on screen rooms is getting an actual bug-proof seal at the bottom of the truck/camper, trailer, or motorhome. It is frequently wide open under that camper, so it’s a fig leaf in regard to bugs. That and the bulk of the screen enclosure is at least as large as the pop-ups, but without the total enclosure to keep out the bugs.
As a former motorhome RVer, we’ve also seen situations where sudden wind ripped up the rooms attached to awnings because that attached room precludes pulling in the awning quickly when those winds came up. Result — awning ripped off too. Big repair bucks!
Be interested to see if anyone else has a different take on this issue.