I want to seal around an antenna cable and joint through an opening that is always damp, so, please, can I use amalgamating tape where the surface it has to adhere to is damp? I have left out all the details of why this is needed, but believe me it is, so please no answers suggesting, or explaining, why I should not be doing it.
Duct seal is commonly used to seal around cables through holes.
Depending on what you're trying to accomplish, this might be a good choice for you.
Most amalgamating tapes will adhere primarily to themselves, even if wet. They may or may not adhere to a wet surface, but if you can stretch the tape around the joint and wrap the tape around itself, the pressure of the tape may provide a water tight seal even if it doesn't adhere to the surface below. This will only work in instances where it's wrapped around convex surfaces, though.
You should be able to find specific tapes that will also adhere to the surface, and possibly in wet conditions if you have specific need for it.
You might also try applying silicone sealant prior to the tape, which will provide additional conformant sealing around the cable. Both the amalgamated tape and silicone are flexible, and good choices for cable entry where some amount of play is required.
Keep in mind that every joint is a liability and requires maintenance - these sealants don't last forever, and should be inspected yearly.