I would not worry too much about condensation in the lines. Condensation caused by shrink wrap is why I hate shrink wrap. Replaced floorboards in some boats caused by poor shrink wrap jobs, and seen too many instances of mold on shrink wrapped boats. It does create a greenhouse, and venting only sometimes works.
As for draining and red pop, I use the same system that our charter fleet does, because it has worked for them for years without frozen lines.
Drain the tanks into the bilge or run the pump if you want. Get the water out of the tanks.I do not put red pop in the tanks as they drain fine with the line to the pump disconnected. I then disconnect the line to the pump, put a new hose on it, drop the end of this short hose into the red pop bottle, and pump away. Once it is primed it goes into the system ( hot water tank bypassed) and I open one faucet at a time until red pop flows. Close that faucet and open it's counterpart. Work through all faucets in this manner. Don't forget the swim shower or anchor wash down if you have them. After one and a half bottles of red pop the system is full of red pop. Turn off the pump and leave it. I reconnect the tank line in the spring and leave the lines charged. Obviously, it will not still be charged in the spring, my system is pretty good at holding pressure, but not that good.
As to seacocks freezing......they won't because they are ALL open for the duration. Splash the third week of April, water temp then about 46 degrees. DO NOT FALL IN!