That is the vid I used. Unfortunately I only had a sharp box cutter and the part I was cutting was a tiny strip so it broke off in chunks but I was able to sand down the edges after. Sounds like you want to silicone the dividers in so that the paper doesn't get wet? Or else you'll have to use a sheet of something waterproof if you don't want to silicone. I don't have mine siliconed in, they were just cut so they fit tightly on their own. Tip tho, cut the corners off the bottom side of the dividers on an angle so that they allow room for the siliconed edges of the tank. That way they don't rip any silicone. learned that the hard way myself. Oh well. Luckily I was able to patch it up fine. I'm wondering now if I should have used clear acrylic because I have been reading that darker surfaces make the bettas see themselves in the reflection. Glaedr doesn't really tend to flare so far at the store so I'm hoping it won't bother him too much, and honestly I plan to put a female on the other side so it shouldn't bother her too much either. We'll see.
Also if you choose to silicone the dividers I can not give you any advice on heating, but if you don't and you leave water in between and slide in something waterproof... sheet of plastic maybe? the tank should be able to be heated by one heater no problem. My tank is still amazingly the same exact temp on both sides and is sitting at a warm 78 degrees right now.
that makes me super happy as that was my biggest fear! here is a pic of the tank right now.
I'm going to add gravel and rocks tomorrow and the plants I have for now. I'll be getting some more decor for them including something to hide in. Shruikan is adorable. He likes to lie in the top of the little flower in his tank. Quite adorable! I'll try to get a picture of that soon!
so here is Betta central in my house right now
(complete with overly inquisitive orange cat, Brutus!) lol