What I would do is to move some water bottles to the top right laying on their side and put a fan in the top right of the incubator- heat rises and you want to push it down. That will leave you room for one tub on top, and one tub on the bottom. For a small incubator you really don't need that many water bottles for a heat sink. Mine is just a hair bigger, but not by much at all and I have 5- 6 water bottles in it.

I just re-arranged mine today and can fit 5 tubs vs. 4 with my previous layout and still have plenty of water bottles.

Old configuration with 4 tubs...


New layout with 5 tubs- I just moved the shelves up one notch and had clearance. Still room for the fan to circulate air...