Traveling in the Cold

Use bottled water jugs to "wash" and a catch basin so you can throw the water out the door. use antifreeze to flush the toliet. no problems.

I have heard of the water freezing and breaking the valve in the holding tanks even with very little water in them. Traveling in Colorado depending where your at could get really really cold. I would use the jugs of water also. But I would put some rock salt in the grey and black tanks and maybe some RV antifreeze in each tank. Then use them with the jugs of water. Some people use the RV antifreeze to flush the toilet in freezing weather. JMHO

Since you said you do not have heated tanks, I'm assuming you are pulling a travel trailer (or driving a REALLY old motorhome). The sad truth is that, if you do not have a TT built with the "arctic pack" ( or whatever they call it these days), you must keep it winterized (and dry) until you get past the freezing weather. Running the RV furnace while traveling won't protect the outside plumbing. Your best option is to carry some gallon jugs of water in the shower/tub to use for toilet flushing/hand washing. What ends up in the grey/black tanks won't cause any issue with freezing. Most likely the inside of the trailer won't drop much below freezing and if it did and the jugs split, the water would be contained in the shower pan. The problem is that the outside of the trailer along with any exposed piping WILL freeze. If yours has a 'belly skin', it probably is only cosmetic and vulnerable plumbing is probably right above it and susceptible to freezing. We put up with that issue for years pulling our TT between Florida and Nevada until we decided we liked RVing enough to take the plunge with a motorhome. Our personal preference is now that and I really do not see us going back. Others may have different preferences. It's great that RVing can accommodate everyone.