One of the purposes of the sunroom is to be able to enjoy the outdoors without being bothered by the bugs. Since the sunroom will be up against the siding there will be lots of gaps. I’m not keen on the idea of lots of and lots of silicone and caulking so this is my solution.
Not even sure if it will work but I’m always game to try something and learn from it. I found a couple packs of foam weather stripping in the workshop. I started with a light grey 1/8 thick by 3/8 inch wide but it was too thin. It was stuck on real good so I left it there and started with the thicker foam stripping. I ran a full strip down, then started cutting wedge shaped pieces about 1-3/4 inches long. One by one, gently put in place and the board was put up against the vinyl siding. Sticky stuff so be sure of the placement before committing to pressing the wedge in place.