If you have propane, you can heat water on the stove (or in microwave) to have warm water to pour down your black water tank to help thaw your black tank valve.
My guess (without more info) is that you should be operating from your internal water tank and you have to switch the valves for that.
If you are going the RV antifreeze route and you have an onboard water filter (clear with elements?) you can pull the plastic cover, fill it with RV antifreeze and replace it. If you leave it about an inch from the top, you should be able to see water flowing into it.
If it isn't...don't bother with the rest of the coach, no water getting from your tank through the pump, to the filter.
I'm guessing your 5th wheel has a complex set of switches for water, antifreeze, etc. Can you post a pic?
We can try to help, but please get us some info to work with :C
Oh, don't fret the cold weather troubles. Learning curve and you will have a great story to tell later, after this is solved ;)