You can use CT100 for the aerial cable and in fact it is recommended for DTT. As it is up the mast I would use a foam core cable such as WF100. The normal satellite cable CT100 has an air spaced core and water can run down it if the outer insulator is damaged or the connection at the mast end is not water tight.
Don't do it.
Much better to get long coax,whatever aerial you use,a few bits of string and when you settle into telly watching mode go into suck it and see mode around the deck.
Been there done it and mast head is not necessarily the best place for aerial,especially if shielded by other boats.
When finished pack away,saves wear on aerial,windage and deleterious effect on righting moment.
Difference between good and bad reception can be a few feet.