You may have to add the twist lock end yourself which is no big deal if you can find one that would work inline like you want to do.
An alternative would be to buy an entire longer cable which would give you 100% redundancy. IMO, that's the best most reliable option. Put it under the seat of the truck and hope you don't have to use it. I only had one occasion that I almost needed more than 25' length. A state park had all the electrical post on the wrong side.
You can always limp by with a regular heavy duty extension cord till you can run in to the nearest RV supply to get a replacement.
IMO, I wouldn't worry about the weather exposure but you can cover it as mentioned or wrap it in a garbage bag. My cord is plugged in 24/7 to the side of my house and has never had issues. You can actually see the prongs, so it's far from weather proof.
Rockwood 2104S, 2014 Ram 2500 Diesel.
USMC 68 -70