Is there some kind of automotive / outdoor tape I can apply to this edge of my tailgate to prevent wear when I load/unload my kayak? The tailgate edge has a plastic cap over it but the bottom of the kayak is wearing it down very easy. Must be a very soft tailgate cap.

 

 

 

Pool noodle?

Maybe try Gorilla tape?

Throw a section of carpet remnant in the back of your rig.

When needed, place it between your kayak and where ever it's positioned in the truck.  

or

Get / make something like this  . . .

https://www.yakima.com/gatekeeper

A-Jay

 

 

Carpet is your friend!!

It’s a truck. If you can’t drive it without a few scratches on it (especially on the inside edge of the tailgate), you shouldn’t really be allowed to drive a truck ?. 
This of course is coming from a guy that uses his truck to haul materials and tools every weekday as a stonemason. 
Seriously though,if it’s really bugging you, just get a piece of carpet like the other guys mentioned. 

You could cover it with one of the kayak keel guards that are self adhesive - just make sure you prep well and clamp it down while the adhesives adheres. But that will also scratch some. I'd do a piece of carpet or cut a slot along an appropriate length of conduit and slide that on the edge before and after kayak.

Flex Seal Tape

 

But seriously, the tailgate protector is meant to protect the tailgate. Your intention is to protect the tailgate protector?

Take a look at garage door flat weather seal adhesive strip like Garade 3" wide X 1/2". You will need to trim to fit and only use a short length.

Tom