The Flatbed needs some minor adjustment. The corners of the cab towards the front are just frame. They need to be windshield or wall.
Actually, what you are seeing is a bug in how weather is handled, not a problem with the truck cab.
When checking in/out, vehicles only take into account perpendicular tiles.
No, Will, I’m not. Weather is checked by checking all surrounding tiles. In all eight directions. I noticed quite a while ago that you can get into the cab of the flatbed without using the doors. That is because the front left and front right of the cab are not sealed. On the semi it has ‘boards’ in those locations. It’s slightly annoying and blocks part of the view. I think these sections on semi’s and flatbeds should be windshields. I will be modifying my trucks to do as I said.