Never mind...I found the answer I wanted on Terry Love. Should have done a more thorough search before I posted here.

Even if you drain the pipes, the residual water in the washer could burst the pump.

thanks, Randy, that's what I learned from the other site, too. Back to square one!

Traps in the waste lines also contain water to block sewer gas from entering the space.

If you keep all the water piping within the insulated space, I doubt you'll have freezing problems with them or standing water in the washer/traps.

I'm assuming insulation at R-19 levels. For your situation the floor/roof should be greater.

Wintertime here often has protracted temps in the teens and water does not freeze in an insulated but unheated shop. During a single digit spell a pan of water ( 'bout a gallon's worth) developed surface crystals only.

The water tank (presumably, water heater) idea isn't so bad, BUT:

If it is radiating, then you are normally wasting power. No doubt a seasonal strategy could be devised.

Unless it's a small tank, you're adding a substantial floor load, a concern from your other post.

Alphonse, THANK YOU!! You made me feel hopeful that this is possible!! I was now (because of all the discouraging info I was reading) imagining enclosing the first floor area underneath and the water heater down there, but I guess if the 2nd floor floor is well insulated, not much heat would be radiating up from the water heater anyway. I don't even have to install a water heater there at all. I have a circulating pump on my tank now and wash mostly in warm or cold water, so piping hot water isn't a priority. Thanks again for the helpful info.