This is my opinion but I don't really like those half logs. Mine wouldn't really use them so I went to square rubbermaid like containers that were about 1.5" tall. (the length and width varied for each snake since one is like more than twice the size of the other) I used a soldering iron to melt a hole on one side and they work great! Love 'em!! One for each side and I'm all set. I got them for like $.99 each. Easy to clean and move around.

If the coconut bark won't hold humidity for you, you may want to try a humidifier for the room or maybe even switching substrates. I think there are several people here who use that and it seems to work for them.

Just remember you won't see half of their activity. You only get brief glimpses into their behaviour, unless you set out a video camera. You'll do fine, so try not to worry too much!