I know exactly the Rubbermaids you are talking about, in fact, I am currently using them for a couple of my bps, including an adult. I have had no problems with mine, but I built a rack around them. So unlike your situation I do not worry about the lids being too loose. I did decide to build the rack with the lids on the tubs instead of having them slide flush with the top because of the "grooves" in the middle where the lid hinges, I figured it was safer to keep the lid than have one of my snakes Houdini their way out.
*As a side note I would have gone with another tub/bin but like you I was unable to find anything appropriate.
I did drill holes in the lids for ventilation. And the lids are fairly secure, I am not as worried about the snakes getting loose as I am my son or niece getting to the snakes. If you are worried that your child may get into the tub without your supervision/consent I do not see a reason why you couldn't drill a hole in the top and on the side and attach a lock of some sort.
As far as securing one end closed... I also weighed this option, but passed on it for the simple reason that it would become a hassle to clean and do maintenence in the "cage", not to mention that it always seems when you want to remove the snake they are always on the "other side".
For heating I use a simple UTH found at the pet store (I believe I bought a medium sized one) along with a thermostat. I affixed each one to the top side of the shelf each tub sits on. That way when I need to slide the tub out I'm not yanking everything loose and pulling on cords.
Of those bps that I keep in this rather simple set up, all are great eaters and appear to be in perfect health, the temps and humidity stay nearly perfect and their sheds are always complete.
For a hide box, I saw many people using cereal boxes, shoe boxes, and various other hides. I have heard that some of the best hides are the terra cotta pot bases with a hole cracked into the side. I live in Minnesota and so anything assosiated with plants is strictly seasonal at best. To find flower pots in the winter is nearly impossible. Instead, I went back to the pet store an bought the largest kidney shaped feeding dishes I could find. I cracked a hole in the ends of these and smoothed out the sharp points and give these to my baby bps and they love them (well, as much as a ball python can love an inanimate object, I guess).
But, you stated you have an adult bp? Try this if nothing else appeals to you: I went to Target for my adult's hide boxes. In the pet section find the CHEAP plastic litterboxes. I mean cheap like $1-$3 they are most likely blue, gray, or maroon. Simply cut a hole in the end about double the width of your bp and about an inch taller. Place upside-down in your Rubbermaid and your are good to go. They fit nicely and are easy to clean.
These bins are not so bad. The snakes don't seem to need much "headroom" - consider breeder racks which do not afford much more room. They also allow for you to access the inside without removing the entire lid. And if you drill your ventilation holes in only one side of the lid you will have a great deal more control over humidity than other caging options. By moving the water dish from warm to cool side and switching which side the holes are on by rotating the lid, you can change the humidity quite quickly and easily.
Sorry about the length, but I feel it's better to be informed and bored than uninformed and lost.
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In the right hands patience, curiousity and willingness to learn can work miracles. In the wrong hands they are mankind's curse and nature's greatest fear.
