60's and 70's? I had ours blown out with Air and then stored it Inside in the St Louis Area.? Luckily we were fortunate to have a heated facility.? Low heat but heated none? the less.? ?Also when below 10 deg we would use lite bulbs in vital spots.
I didn't have a motorhome back in the early 70's but I did have a large truck camper. I winterized it by draining the watertank, hot water heater, and taking the lines loose at the waterpump and blowing them out with an air compressor, same thing I do today with my motorhome except I use the city water connection.
We started RV'ing in the 70's with our parents and have continued thru today. We used motohomes for our travels. The first one was only 22' long. Before the current anti-freeze was available we blew the air lines out with compressed air. We would let the system sit for a few days and blow it out again because the small water drops that remained would collect at the lowest spot. We would repeat this several times until the air coming out felt dry. Any remaining water that froze would not be enough to cause a pipe to burst. Copper pipes were most often used for water lines. Plastic was used for the drain lines. For sink traps, they too were blown out then filled with an alcohol mix or an automotive anti-freeze. No indoor storage was used. That method worked well, only had a pipe burst once. Of course it was in an area that had no access. We had to cut open the wall, fix it, and made a decorative patch.
Today we blow the water out before pumping the anti-freeze thru only once. That way we see less mixing of the ant-freeze and water, thus less antifreeze is needed and full strength is maintained. Our unit is 36' and with a hot water by-pass we only use 5-6 gal to winterize. That method has not failed us yet.
Store it in Southern California and tow it only to the deserts in the winter?? ? I'm like Tom, I live in coastal California and I have little idea on how to winterize anything.
Theorizing it a bit, with a trailer it should be fairly easy.? Drain all the tanks.? With the freshwater system opening all faucets first to back drain as the tank drains.? ?Pour a bit of regular antifreeze into the various drains to protect the P-traps or blow them free with a compressed gas drain plunger.?
Charge the batteries full or better yet remove them an store in a heated area on a plastic mat and hooked to a trickle charger.?
But then what the hell do I know ---? if the LA Basin ever got a hard freeze, the glaciers would be overrunning Michigan and New York.? ?;D
We had m/hs in the mid 70's and the sugar based pink fluid was available then. WE did not use ethylene glycol in RVs.
The problem was that it did not protect you to very cold temps unless it was full strength so I blew everything out and used a small amount in both tanks to protect the valves, the toilet, and the grease traps in the sinks. I used to completely remove the pump to drain it as I had no easy way to prime it with antifreeze.