Antipodes, I used to make it until a couple of years ago. I used a 5 gallon stone crock, cover it with sterile muslin, then put a plate on the top which should be just under the fluid the cabbage lets out( after about 1 day). Put a weight on the plate. I used to use a canning jar filled with water .You need to skim it daily to remove the scum which will weaken the brine if left there,and at the same time change the cloth and the jar. Needs to be about 70f while fermenting but after it is done it is better to be kept much lower at about 35f. The plate should be a fairly good fit in the container.I had a wooden lid on the crock.
Keep a close eye on it, if it gets slimy, chuck it and try again when it is not so hot. Under 68f fermentation will be slower, over 72 and you risk it spoiling.
It will bubble while it is fermenting, when it finishes it will be a clear pale colour.
Types of cabbage are important too, and be sure the salt quantities are accurate.
Good luck.
XX Jeannine