I will have four joints to weatherproof where the wall panels butt up to each other and have been scratching my head on how to do that without creating more hardware. The gap in these joints varies from zero to about 1/4". I found an item online called Shurtape Floormate. It is a plastic tape that comes in white and is used as masking tape and temporary gym floor markings on hardwood floors. It comes in 2" wide X 50 yd rolls and only costs about $10.00. It is a low adhesion material that is supposed to be good for up to 30 days and will peel off easily. I bought a roll and am running a test on a short section on two of my panels. I plan to leave it on for about three days (typical camping period for me). If it works, I plan to simply seal each of the four seams with this tape while camping. It will be much easier than dealing with a mechanical seal like a tee bar, rubber seal, or a velcro panel. I figure it will take about five minutes to cut and apply the tape on each trip and 50 yards will last me for at least 7 camping trips. The white color will tie in the white of the top and the bottom shells.
This is available on Amazon for about $10.00
Short test piece inside the garage. If this works, I will do another test outside where I can see how it works in the heat of the sun and water.