Hi Chris!
Nice boat name! Water of life indeed....
As for keeping your mains'l SLUGS in place, I personally don't think one needs a mast gate. Either use a track stop right above the slot :
https://www.davisinstruments.com/produc ... rack-stopsOr simply tie a line around the mast above the slot, even an extra sail tie will do. FWIW, I tie a Larkshead, around the whole mast - start by pushing the bight of your Larkshead thru the gap between the luff and the mast, pull the tails thru the bight, and Bob's your Uncle!
Of course my method means that you'll have a somewhat sloppy "bundle" if/when you flake the main to the boom. But for "douse the main, motor to the dock," who cares. Same for leaving the dock to make sail. You can make it all neat later, if you want/need. But if you're just trailer - daysailing (ie pulling the boat out after each sail), then consider taking the boom off the mast and simply wrapping the main around the boom. Better for your sail as compared to flaking it down.