While it's true, you don't have to use bolts with the Pro Product one, I wouldn't want to just use wood screws or something like that. Its not exactly light as its an aluminum body unit. The RBI ones can get away with it since they are ABS body and a lot lighter. But to each their own. And you don't need a divider for a 4' cage for a sub adult BP. In the wild, they don't live in a 2x2 section of termite mound or a rodent den. The key is to clutter up the cage enough with stuff to make them feel secure. That means more than just 2 or 3 hides with nothing else. Sure, in that case they probably wont be happy as traveling from hide to hide will be what will scare them as it exposes them. Now throw in a few hides, some silk vines from a craft store like Michaels and maybe a couple paper towel rolls and he will feel a lot safer traveling between hides. I've started lots of snakes in big cages and never had a problem as long as you give them cover for the whole cage, not just a few hides.

Some BPs will climb. Mine loves to climb all over and will actually perch on top of her PVC toy/tree thing I built her. A few other people I've talked to about my BP liking to climb have also told me theirs likes to climb all over as well. its kind of like people saying boas are terrestrial...well yes kind of but if you give a boa a branch, shelf or perch, they will make use of it. Now it's up to you OP if you want to get a shelf but for $30, its worth it to give them the option imo. Just remember when you mount the RHP, don't mount it over top of the shelf or you will run into the problem Chrid is having.

Also for the RHP, if you call Pro Products and talk to Bob, he will probably set you up with the PH3 65 watt one as that seems to be the go to one for 4x2 cages in a mid 70s room. Or get the 80 watt one from RBI. It really wont matter as the T-stat will be controlling it. Just remember, a RHP is not going to work like heat tape and heat a single spot on the floor unless you put something down like a piece of flat slate or something it can heat under it. They are designed to heat an object under them which in turn gives off heat to heat the air.

The way I set my RHP and t-stat is I put the probe on the cool side about 2" above the substrate and then set that to 80F. That gives me around an 86F or so warm side. This is the way Bob at Pro Products says to set it up too. Some people will set the probe under the RHP about halfway down and set the hot side. Problem I see with that is the cool side can become too warm and then your snake has no where to go to cool down. Bottom line is you will know when its set right when the snake thermo regulates. If it is on the cool side all the time, you need to lower your temp. On the hot side all the time, need to raise your temp. I would just avoid setting it on the floor because if the snake pisses on it, it could destroy the probe and then you will need to get a new one not to mention it could give false readings. This is for the BP. For the carpet, I would definitely get a shelf and me personally, I would go for something higher like a T12.