Split loom or spiral loom, either way, but a real plastic protective sleeve to go over that cable and prevent chafe from the hole in the mast. Under ten bucks will buy you at least six feet in any auto parts
store. Eiter one can simply be wrapped around the existing cable run, and then secured with black (UV resistant) tie wraps, or butyl tape.
The only problem that I can see with drilling right into the conduit, might be that the cable has to make an acute bend to get into it--and acute bends tend to become failure points. If it isn't a force-fit, and you don't have a chafe problem, you should be OK.
Do put a "drip loop" in the cable (it should go down and then back UP to the hole, not simply down into the hole) and use something like "coaxseal" to plug
the hole against further moisture instrusion. That's another black butyl(?) putty sold in Radio
Shack (sometimes) and electronic supply houses. Any other caulk would make a good second choice.