In 20+ years of owning boats I've never run antifreeze through for winter storage, & we've had -15C up here in the frozen north. If it's an Etec, it will self winterise, just follow the instructions in the owners manual. Wash the powerhead with a low pressure hose & let the water run down inside the cowls to flush out the salt. I always add Evinrude 2+4 conditioner to the tanks & fill them to the brim for winter. Put the battery (ies) on a good charger (eg Cetek) & leave them on float through the winter. Make sure the trailer is WELL rinsed, including the hitch, brake drums & inside the box sections if you can get to them. Check the tyre pressures, if poss block up the trailer on axle stands or wooden blocks to take the weight off the tyres. Light the fire, pour a dram, get the dog in & settle down for the winter. Plan next years trips & spend the next few months talking bollix on Ribnet.
Rule#2: Never argue with an idiot. He'll drag you down to his level & then beat you with experience.
Rule#3: Tha' can't educate pork.
Rule#4: See rule#5