Starting early and protecting against freezing

I’d like to start wakeboarding next month but in my part of the country there is a chance for a late season freeze all the way through April. One meteorological chart I looked at shows freeze dates for 9:10 chance, 1:10 chance and last of the season. Surface temperature can be lower then air temperature. The temperature data in this table is measured 5 feet above the ground. So I expect that the dates in the table are optimistic – i.e. predict a safe date perhaps before it really is.

How do you deal with the risk of a late spring freeze on an inboard? For full winterization I’d have my dealer run antifreeze through the engine, but I don’t think that I want to go to the dealer all the time.

There are several drain plugs in most engines. Is it reasonably safe to pull the plugs and just let the lake water drain out? Do you need to pressurize the cooling manifolds to blow out water trapped in low areas?

I’ve heard of self regulating electrical heating elements. The heating elements turn on when it’s cold and back off when a safe temperature has been reached. I could run this kind of heater off of my second, isolated battery, has anybody tried that?

Thanks!