We're on our third set of weaners now and generally just add a little more straw on top when it looks a bit thin. They seem quite happy and have no problems sleeping in there at various times of the day!
If it all looks clean, dry and smells okay that's a pretty good guide for me and our pig ark is just on the ground in some woods (rather than concrete).
I have come across some who say you should disinfect a pig ark on a monthly basis though! Maybe I've just been lucky so far or perhaps my Tamworths are just very healthy pigs?