HI, and welcome to the HCA.
Using a pop bottle to isolate molters is only necessary when something has gone wrong. For example, if you have a surface molter you would use a pop bottle to isolate the molter from other tankmates. If he has dug down and the substrate is deep enough (judging from the picture it looks a little shallow, it should be around 3 times higher than your largest crab) he should be okay. You just have to remain patient and don't bother him.
On a side note, I see a few things in you tank that need to be removed.
First off, the sponges. Those will collect bacteria unless they are cleaned constantly. Besides that, they don't benefit the tank that much.
Secondly, those painted shells are bad for hermit crabs. The paint can be toxic if the crab eats any of it. Sometimes crabs will chip off the tops of their shells to get a better fit. Since hermit crabs are scavengers, they could potentially eat any chipped off paint.
I hope this helped
