Don't know if this pic will be of any great help but just to show you what one of our big Rubbermaid tubs looks like open. This tub is quite large as the snake pictured in it (Brannagh) is over 2,200 grams. The lid for this tub also has ventilation holes melted in it (a cheap soldering wand is a wonderful thing LOL). You'll just want to fiddle with the number you need dependent on your own humidity in the room the tub would be kept in till you get it steady around 50-60%.



There is normally also an Acu-Rite in each tub (I'd just cleaned this one so hadn't put it back in yet when I snapped this pic). They are a nice, reasonably priced digital unit that will give you two temps plus humidity for around $11.00 (Walmart, also Lowe's and Home Depot but under different brand names).



Plastic tubs aren't the prettiest enclosures but they are super easy to maintain and BP's do very well in them. You want to go for more floor space than height as BP's aren't big climbers and a very secure lid (reinforce if needed) as all snakes are natural escape artists.