I will only use Butyl tape, PLAS-t-COTE and ProFlex.
I have bought the Butyl tape from several different RV supply stores, but have had clerks try to give me the clay type tape.

I have bought the PLAS-t-COTE from RV supply stores and Box hardware stores.

I purchase ProFlex from RV supply stores. It is great, but very difficult to remove, and does not bridge gaps very well. It easily goes into cracks. I have used the white, black and clear.
My 1988 Bigfoot was sealed with Butyl tape, PLAS-t-COTE and Silicone. All of the Silicone has failed years ago. It was only stuck where it was not needed. I have had no failure with the PLAS-t-COTE. The only failure with the Butyl tape was poor application, as can be seen in the following photo.
