Fifth wheel caulking issue with it staying tacky

What ever you decide to use, may I suggest you try out an application experiment first. Apply some sealant / calking to some scrap material and come back a couple days later to see how it turned out.

Several years ago, I used a brand new tube of caulking on a shed and it never did cure, I had to remove it (Big Mess) and start over.

I was rather agitated to say the least, so I called the manufacturer and gave them the lot number and expiration date on the tube. The customer service rep told me that with all the new environmental rules and regulations, the chemical formulations have changed significantly over the years.

He told me, even if it is a brand new tube within the expiration date, "you should always test it out before applying it to your project"

And, if the tube has been opened before, partially used and saved for future use, it is even more likely for this to happen.

In the old days it was not uncommon for calking to dry up and harden in the tube. Now when it goes bad, it does not dry / cure correctly.

I have had this happen three times in the past fifteen years or so.

Good luck