A little insulation philosophy.....
Insulation does not heat or cool anything, it merely inhibits the transfer of temperatures from on side to the other. It is a timing thing. Instantaneously it works great. Over time the insulating material will cool/heat heat up to the ambient temperature.
If you leave your water tank outside for a lengthy period of time in freezing temperatures, it will freeze up-- (insulated or not)... guaranteed. Only heat will prevent a freeze-up for long-time storage.
Oh well....just thinking out loud.
Thanks for the replies guys...I am outside in Moab Utah going through an unusual bout of very cold weather. First my fresh water system froze up...I opened up all the interior access panels and put a small fan there to circulate warm air from the RV through the pipe spaces, in about three hours that problem was solved.
It is much warmer here today and I tried to dump the grey and black water tanks and there was a chunk of ice in the outlet area, I cleared that and hooked up the hose and of course nothing came out. So I have to assume the tanks are frozen. Black water is basically empty but the grey water is full...there is water in the shower/tub since that is the lowest drain, it backed up into the tub. I emptied that with a bucket, have a silver reflecting space blanket under the trailer in the bright sun and a small electric heater with a fan blowing into the pocket I have created with the space blanket around both the grey and black water tanks.
Before the sun goes down today I will try again to open the valves and see if they empty, if not I will keep the heater on all night and try again tomorrow.
I have a solution for the long term - I will install tank heaters for the waste tanks and I have already wired for small electric 12 volt fans for the access panels for the fresh water plumbing areas inside. I will put them on a switch and turn them on to circulate warm air from the RV into those plumbing areas, should work fine. I ordered 4 muffin type fans low speed and quiet, kind of like computer case fans. They will panel mount nicely and be unobtrusive.
So I think I am squared away on the long term as I occasionally hang out in cold areas, I am from Alaska and will be taking my rig up there next summer and it can get cold there even in the summer, so we shall see!
Hopefully what I am doing today will get them empty and then until I get the heaters installed I will not use the tanks much if at all!
Thanks for the replies...