how many holes per tub?

I'm getting a CB70 rack from RBI soon. Just wondering how many ventilation holes I'll need to make in each tub?

I've not made any in mine...

as many as neccessary to maintain proper heat and humidity with in the tub....

Just remember to let it sit for a full day or so to see where your humidity is. It takes a while for it to get where it's going to settle.

Set up your tub with all conditions minus the snake, ie: heat, substrate, water dish, hides etc.

Allow your temps and humidity to stabilize for roughly a day.

If your humidity is too high, start by adding a row of holes around the container.
Allow to stabilize and recheck humidity. If still too high add another row.

Lather, rinse, repeat until you get your humidity levels right where you want em.