Coax-Seal is a brand name, and good stuff. Self amalgamating tape, butyl-rubber, self fusing silicone, all good choices.
Industry standard is to torque the connection to manufacturer specs.
Test and make sure it's good.
Put a layer of electrical tape over the connection. Start low and work up, do a "half lapped and back" wrap, where each wrap of tape overlaps half the previous wrap. Work up towards the antenna, then reverse direction and go back down to the starting point.
-make sure you don't cover weep holes on antennas, those are necessary to allow condensing moisture to exist the antenna, they are usually well marked by the manufacturer.
After the tape layer, overwrap that starting at the TOP and working down and continuing a bit down past the tape. Overlap each wrap.
Work the tape together with your fingers. This should allow you to mold it evenly over the connection.
Often another layer of electrical tape over that using the "half-lapped and back" procedure above, covering all the sealing compound is recommended.
I've got one contractor that follows all that up with a coat of "Scotch-Kote" sealant to seal everything.
Done right, the connection will be protected from the environment and won't have any issues. I've seen 20-30 year old installs come down and the connections are still bright, shiny and clean with no issues.
Big issues people have is they don't cut electrical tape. They'll grab it and pull until it breaks and then complain about "cheap tape". What happens when you do that is the plastic tape stretches and spreads out the adhesive too thin to work. The end of the tape will quickly start unraveling. Always cut the tape with a pair of scissors or a sharp knife.