avgas

I have a feeling you are looking for the foam in this kit to seal up the big gaps at the top of the box. https://www.accesscover.com/access-total-bed-seal/

I had one bad sensor on my 2017. Every time I would wash it or drive in the rain I would have issues for a day or so. I took it to the dealer and they couldn't find anything wrong, Went back to the car wash and got the same problem. I took it back and showed them the pics of the messages I was getting and told them to wash the truck. They ended up changing one sensor and all has been fine since.

I have had problems with mine as well. I have had mine to the dealer and they replaced the HMI module i think. I still have issues and it is frustrating. Same thing happens to me. Sometimes it connects fine and the next time its crap. Sure would be nice if they would come up with a system that works.

For some reason people who wire trailer plugs do not think they need to connect the ground wire. The ball just doesn't provide a good enough ground. Check the trailer ground, Its likely the issue.

My iPod works like crap as well, it goes into shuffle on its own shows the wrong song on the display ect. If you look at the list of compatible devices you will see they are all old iPods. This system needs an update big time. I had a 2014 and it worked way better than the 2017 I have now. I am not happy with the stereo in this truck at all. GM should be embarrassed to have released a product like that!

Have a look at this previous post. There is a nice pic of the 50 amp fuse that you move over from one set of contacts to the other. http://www.gm-trucks.com/forums/topic/156867-12v-accessory-power-outlets/page-2

I took mine in on Wednesday and so far the issue is gone. They installed some shims and added clips of some kind. Both front seats were moving and both seem to be repaired.