It will be fine. Don't give it a second thought.

Put it in the water.

Like Griff said,don't worry about it...it's fine

The electric blanket method works well...and yes seal up any points that air can get in or out.

These are all stupid answers you are getting.....for the half hour or so to drain the water, do it, rest peacefully and have a few beers,..If you want your boat to catch fire put the light in.....do yourself the right thing and drain it.

A small light bulb in engine compartment will hold temperature up. Also for your peace of mind stick a water bottle in the engine compartment and another on the swim platform. When you find they are still in liquid form in the morning you will feel better!

You can drain it in less than 5 minutes.