Best way to connect stacked bins?

[Vespertine]

I'm looking for advice on the best way to connect two stacked bin cages. Hammy number one has two bins side by side which works wonderfully but I don't have the room to do that again this one needs to be stacked.

Both bins are 30cms/11.8inches high and I'm happy to add a shelf or ledge to the bin so the climb is less steep or can be done in two sections.

What would you guys use to connect them?

[CMB]

Would you be able to make same setup for the new cage and stack them on top of the existing setup?

Side ventilation would be needed on both setups.