[AmityvilleHams]

I personally wouldn't combine two Detolf units length ways to make a very long narrow enclosure unless you had robos or Chinese hamsters, because then the width wouldn't be an issue with those species, and even with the other dwarf species(including hybrids) it would be decent enough. However, a single Detolf would be adequate in that case.

A pair of Detolf units combined in the width direction to make a cage of the same length yet twice as wide would be a lot better when it comes to making a Syrian cage, but you'd want a raised lid so you can actually have enough substrate depth including a 12 inch wheel. Aquarium silicon would work to seal the two units together but you'd need internal bracing which would also keep things structurally sound, however silicon takes at least 48 hours to cure and would need to be in an entirely different air space than pets as it does produce toxic fumes while curing - preferably outside which is understandably very inconvenient when dealing with such a large cage as a double Detolf!