The good news is RT management has been presented with a simple solution to your issue, which is also one of mine since I too have a factory generator in my RT. In the meantime you can install a simple part that is available at most auto parts stores and online stores. It is a heater-core back flush tool. What is it? A simple T fitting that can be installed in your water feed lines. 3/4 or 1/2 inch barbed fittings on two ends with the 3rd T fitting using a garden hose connection. Good for two things. You can just simply drain the water out if your choose or close the seacock inlet valve, purchase some clear 3/4 inch ID hose from your local hardware store. The longer the hose the less need for two people.
Fit one end of the hose with a garden hose repair fitting that fits the flush tool T. Now take the cap off of your $10 a gallon (not alcohol based that can damage rubber seals) Drill that cap and place another 3/4 inch barbed fitting in the cap so the new hose can be attached to the top of the cap. Many options available at your hardware store too. I think you are following me now. Screw your gallon of antifreeze on the hose and turn it upside down. Now crack open the fitting on the flush tool T and poke a little breather hole in the bottom of the jug towards the outside edge, watch until the antifreeze reaches the T by watching through the your new clear hose. When there, tighten hose fitting. With a long hose you can start your Gen and then walk to the side of the boat and watch the Gen water outlet for antifreeze coming out. Feel the weight of the antifreeze jug and when it feels like it is getting low, shut off Gen and install a new jug to your tool and restart Gen. Save that used jug to poor the other leftover antifreeze into from other bottles if that much is needed (just put new cap on used jug and set on it's side with vent hole up so it doesn't spill). When Done feeding with antifreeze, turn off Gen, turn jug upright, unscrew lid, put finger over hole to hose to stop siphon and then quickly remove other end of hose and replace cap on flush tool T. Done, very little spill into bilge where bilge pumps have rubber seals. Just know that the water line below the spot you install the new T will only be protected by mixing with the antifreeze in your line above the T. Seacock inlet valve and above to water line will likely be protected enough as long as the water your boat is floating in is not frozen.
I see where you live and the temps look very close to where I live. Tuesday we had a low of 34 degrees, but now is warming up again and many good days to boat still coming. If you choose to to go out and want to use your generator again, guess what? Yep, do it all over again... I plan to put several in my boat, already has one inline to the A/C, and few more shut-off valves so I can isolate Gen, A/C reverse heat, fresh water wash-down and the head. I can still boat without those items being operational and even fresh water if I carry a few gallons of antifreeze to help flush the toilet and protect waste tank. I want to be able to use the generator because that gives me many options for power, heat and battery charger if needed.
The more you can use you big investment throughout the year the more enjoyment you will experience. The good and bad news is, if your boat gets used only 8 months out of the year it might last say 10 years, but if you use it 25 % more each year it might only last 7-8 years. These boats are built to use and enjoy.
JFYI, my boat is an OB model so no inoard engine to worry about isolating or protecting.
