@oddball this is what I used under the bed rail. I got it at Home Depot for like $5 for a roll. It’s super thin and very sticky it’s Also flexible. It’s pretty cold here on the East Coast so what I did was took a torch and very lightly heated the top of bed so that the adhesive would take better. Then after it was applied I took a razor knife and cut just a small enough hole so when I put the cap back on the clips would go through it. Also before I put the cap back on I ran two to three lines of Permatex On top of the rubber tape on each side. I went to advance auto and found a caulk tube size of it for $20. I went with the very flexible permatex. It’s your choice but I also removed the bulkhead rail and applied three or four lines of Permatex under there also. And for the left and right corner where the gaps are behind the cab I used some duck seal also in the gaps also Got it from Home Depot. I slid the end caps out until they touched the side. Then then jammed the duct seal up in the hole from underneath. Then I ran some Permatex over it all for extra measure. Don’t remember if I read it here or over at Tacoma World but take a flashlight and laid on your bulkhead corners if you can see light coming in that means dust and water will get in. There is also 2 1/4inch gaps at the back of your bed on the floor you may want to fill those too. In the picture with the stiffeners you can see the Permatex in the corners. And then finally you have your little box cubbies in the bed you may want to seal up too. Also invest in a set of bed stiffeners to prevent your bedside from bowing out once you get your camper on your truck. I went with the total chaos stiffeners because they come all the way up to the top rail the other ones on the market only come only halfway up the side. I also wanna give a big thanks to everybody in this thread for all the tips and advice they gave me.
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