Does anyone have a good way of tying down a mast to the gin pole? To keep it from sliding down I wrap it several times with the rope or tie down. However it still slides some making it very tight and difficult to undo.

Why would you need a gin pole on a Hobie 14/16? These masts are very easy to raise by hand. Just stand as far back on the tramp as you can to maximize your leverage when you do the initial lift.

I assume that you mean the mast support on the trailer, not a gin pole for raising the mast. If that is the case, try lining the inside of your support with closed cell foam, or some material that isn't slippery. I use standard black rubber tarp straps to hold my mast in place. The constant tension on the foam keeps mine from moving. On longer trips, I do tie a rope around it in case of a strap failure. Maybe you should look into a rear support also, if you aren't using one at this time. The heavy plastic type that Rick sells (mast-caddie) work very well and will eliminate any slipage.
Go the the catsailer.com store and search for "mast caddie".
If by chance you really do mean the gin pole that is used to raise the mast, I use 1" wide strap and velcro to hold mine in place.
Good luck,
Jack Hoying
Fort Loramie, Ohio
Prindle 18 #1645
http://www.bright.net/~jmhoying/sailing/prindle.htm