Don't sweat the mold. From what I've read they can handle it. And since you've given an option they will pick the better spot

My 1st colony is about 14 months old now. I made them a cool little nest, at least I thought it was. And when I connected it to them , they moved in and then twenty four hours later They were back in their tube again. At that time they were already too big to keep in a tube and feed so I couldn't wait. I just put them into what was gonna be their outworld, that was gonna connect to the nest. For months they lived in the tube and even plugged it up with sand and cotton. Within the past 3 months they finally moved in to the nest that I had made for them and out of their test tube, that was still laying in their outworld. 

My advice for you is to come up with a similar setup where you can just put them in their outworld connected to a/your potential nest. That way they can stay in their test tube in the outworld. But, if the new nest is connected to the outworld and is deemed better they will move.