Some people have joined two bins together
ie cut the end off each and join them together - but I believe that means some heavy diy like soldering.
The bins on their own aren't a bad size but really aren't deep enough to give good floor area. 30" is just about ok if they were deeper. Internally they will be quite a big smaller as they slope inside.
For now I would scrap the burrow box and just have the set up between the two adjoining bins to make the most of one of the bin floor areas. So have the house, food water and the odd toy in one bin and the wheel and a digging area in the other bin.
It isn't ideal as it means they have to use the tunnel to get to the wheel (whether they want to or not) and they don't have much foraging space. Their normal behaviours at night are usually, snacking, pouching, exploring, foraging for a bit. Then a rest in the nest, then quite a bit of wheeling, then more foraging, hanging out and snacking.
If they can do all of that in one larger area they can have normal behaviours. It's a bit like us having to go next door to a different house to do the washing while cooking in the other house. Not quite natural.
Which country are you in? There are bigger bins available (a lot easier than soldering two together). Or a detolf.