I have camped many many nights below freezing. I gallop it was 9 degrees and water did freeze to no ill effects.
I put antifreeze once and will never do again. It is a foamy pain in the ass.
When below temps all day I run tank heaters all day.
Do you have the ceramic filter on your Karavan? My understanding is that since it's external on Kruisers, it can freeze and basically explode due to expansion.