I think by having a raised floor I can keep the floor on the inside unobstructed by joinng the halves under the floor and with the supports on the front, back & top.
I was going to mention this idea in my previous reply but decided not to. The biggest issue here is having a lower slot for a divider to slide into. If you use some sort of shim for a natural separation between the halves then that can become plugged with substate and/or dried urates or deficate. Not good.
Or you can just have some sort of moulding on each half that acts as a slot.
Problem I'm having is figuring out how to keep waste minimal for a 10-ft cage since I've been unable to find anything in 5-foot lengths except for 1/4". Make it 12-foot long? How about 16? LOL!!!
I also hate creating waste, but if you use Sintra I think you'll find the scrap useful for various things. Maybe build an incubator or small rack that you can sell locally to help defray some of the costs.
Give me a size range of what is acceptable to you for the cage. Something like "no smaller than" 10 x2 x 1.5 and "no bigger than" 12 x 3 x 2.5, or whatever. I might have some ideas.
Obviously you're welcome to take this to email. I think you know where to reach me and I certainly owe you 
I like the dowel or pin idea the best. I don't really need a cage with a divider but there are times when it would/could come in handy. Maybe have it to where the end wall that stops the glass, on one side, could be removed by a removing a few screws to allow the glass to recess far enough.
I like dividers but am a firm believer that they need to be easy to use or they won't be used. Well unless you want a cage that can be semi-peranently divided in half, but that does not seem to apply to you. I'm not sure I'm following your idea, but it sounds like a few to many steps to take to allow you to put a divider into a cage of an otherwise tame snake.
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Current snakes:
0.0.1 Gonyosoma oxycephala - Java locale (green)
1.2 Gonyosoma oxycephala - Jave local (green)
2.2 Gonyosoma janseni - Seleyar locale (all black)
1.2 Gonyosoma janseni - Celebes locale (Black & Tan)