Its about an inch thick with a small drop down to catch the lid that came with it. Wife was surprisingly okay with the bookcase hob side idea. Ill have to find something.How thick is the rim? If you can fit a HOB overflow box on the side of the bookshelf where u currently has the heater, then you can run that down to under the tank where it look like you should have room for a 5 to 10G tank to DIY a sump/fuge.
If you can't figure out a way to run a hob overflow box. Then wat you can do is, keep your canister, remove the mechanical filtration (or keep it, doesn't matter at this point since algae reactor will control no3 absorption) , plumb an algae reactor next to it, connect the canister out to the reactor in, and connect reactor out to the tank return line.