holes in tubs, how far apart?

I'm getting ready to put all my ventilation holes in my tubs, how far apart should they be?

I am doing the same here, i have two tubs the size of shoe boxes!

how ever far you want them, you're the one that has to look at it :)

i use a scrap piece of 1/8" board and drill holes an inch apart then i use this as a stencil for my soldering iron.

I have one row going all the way around the tub that is spaced ~1.5". I get good humidity and plenty of ventilitaion this way.