I like to use the 3M ScothKote material for waterproofing connections. It was designed to make directly submersible waterproof connections with the 3M tapes.
I was initially introduced to it and taught how to use it many years ago by a good ham, and Motorola field service tech, Bob, W6NZX (now SK).
As many have observed, it is not UV resistant. It was NEVER meant to be UV resistant, nor used in a manner that would expose it to UV degradation. Others have reported problems getting connections, made with it, apart. That's a good sign that it does bond and form an effective seal! It was developed to form an almost forever underwater seal, but can be used to get the same highly reliable seal, without great drama during periodic disassembly. As with many other things, what one uses is often not nearly as important as how one uses it.
Here's how I use Scotchkote to avoid the problems cited by others:
1) Tighten coax connectors and make sure that the exposed surfaces are clean and dry. I first put a teeny swipe of silicone grease on the center conductor pin and push the connector together several times twisting it to spread the grease, this insures that any moisture that may make its way into that location will have to do battle with something several times more stubborn than it to deteriorate the contacting points. Another dab goes on the mating threads that gets spread as the connector is assembled.
2) Wrap the connection with 3M Super 33 or 88 electrical tape. If the coax is not horizontal, wrap the connection from bottom to top with 1/2 the tape width overlaps. This makes the tape wraps form a shingled overlay with their exposed edges facing down. This reduces the chance for water, running down the cable, to impinge on the exposed overlap edges and work its way in between the overlaps.
NOTE: Remember, water is one of nature's most prolific solvents, and can make its way almost anywhere we don't set ourselves up to gain an advantage against it! This is a molecular structure problem, that we have no control over. There are very few "truly waterproof "materials, things are really just more or less water resistant. Wrapping the tape the right way just presents the water with a more difficult path (it has to run uphill) to make its way into the connection.
The tape wrap should extend 1-2" past the connectors onto the cable jacket, and all the wraps need to be pulled and formed to not create any wrinkles in the tape. ALWAYS cut the terminating ends of the tape with a razor knife or side cutting pliers (DO NOT break it by pulling till it snaps off), then allow the free end to relax a bit before laying it down.
3) Coat the wrapped connection with the Scotchkote. You don't need gobs of it! Just a fairly uniform even coat. This is sometimes difficult to do on hot days, because the material has a low boiling point solvent vehicle, which evaporates very rapidly. On hot days, you need to have a fairly full brush load to quickly apply and spread all over the area in a continuous coating. After you've done a few you wll get the hang of it, and it is not disasterous if you have to make several applications to get it coated. Just try to get is spread without a bunch of bubbles and blobs and craters. The coating application should extend past the first wrap by 1-2". Allow the coating to air dry till it is firm, but slightly tacky (no transfer to your finger when you touch it, but still feels a bit tacky)
4) Wrap again with tape as described in #2, with the tape entirely covering the coating that extended past the first wrap. At the terminating end of the wrap, I cut and fold the tape back against itself, to form an easily identifiable tab, to be used to unwrap the connection. It may flap in the breeze, but will not unravel because it has been bonded to the jacket by the Scotchkote.
What has just been described is not the forever Scotchkote connection. It is the almost forever, serviceable Amateur connector connection.
Here's how it works:
The first tape wrap provides a barrier layer to protect the parts in the connection from having the Scotchkote bond directly to it. This has been the source of many complaints about using the material. It helps provide another sealing barrier, but is really there for convenient disassembly.
The real seal is formed by the coating layer that goes from cable jacket-to-jacket across the connection, and its bond to the outer tape wrap. The outer tape wrap covers the coating material, protecting it from UV exposure, while forming the bonded seal.
I have had zero connection failures in ~20 years with this type of seal, and essentially no headaches (that may be relative) getting them apart. A one or two year old connection comes apart by just pulling the tab, its easier with the heavier 88 tape as it is stronger. When I moved here, I had to take apart quite a few 10 year old
connections. They had to be scored with a razor knife in a few places to peel apart, but were not very difficult, and the stuff inside was still shiny new.
There are newer high tech materials and methods for sealing connectors, and I would not say one should not use them, but good old Scotchkote, for ~$5 a can, that seals 50-75 connections, is still a very reliable Cheap way to do it.