I would recommend buying an antifreeze tester to make sure the fresh water radiators of the engine and Genset are at minus 20 or so. It doesn't matter if you flush the seawater side, if the interior loop isn't protected.
I have not found a tester to test the 'pink rv stuff' for freeze protection. It is not glycol based. BUT, it is really cheap. So, in My opinion, more is better. Err on the side of caution.
I use my pink stuff to flush the fresh water system. I catch ALL of it after I have blown the lines out with compressed air. Then I reuse the 'used' stuff as an initial flush for the AC system. Then flush the AC system with a gallon of new pink. I catch the last gallon of pink from the AC and use it in the generator. Then flush with another gallon in the Generator. Catch the last gallon and use it to flush the Engine. Then use 3 gallons to flush the engine until all the water coming out the exhaust is pink.
My sea strainers have removable lid. These are conveniently just oversized to use 12 wraps of electrical tape around the threads of the bottle, and a quick tip over and I can step on the bottle and give a 'power assist' to the pink stuff on its way.
BTW, The earlier question about 'sea chests' refers to a valve on the water intake hose. If you really don't have a valve on EACH and EVERY seawater intake hose (below the waterline) you should have them installed.
Speaking as an ex yachtyard worker, many (I mean MANY sinking, swamping, or near misses) are caused by below the waterline intakes that (even WITH valves) are not shut, when the boat is not in use. This is a FATAL mistake made by a majority of boat owners who routinely leave underwater valves open. This is not just a idle topic, but valves that are not used regularly often get seized up, and need large efforts (or shipyard haulhouts) to make them right (loosening up or replacing)
If you do have the valves installed, use them. Use them regularly. They make flushing easier, and allow you to use the valve to force the pink stuff in the right direction. The only thing to remember, is to open the valves once you are done, to let the water drain out, so nothing freezes in the valve. Just make sure you close them, so critters dont crawl in and make a nest. That's a 'itch' to clean out next spring.