If you already have the aquarium-style cage and you don't want to get rid of it/can't return it, there are still ways to keep the humidity up. I mist mine a couple times a day with a spray bottle and keep a damp towel or tshirt on top while my BP is shedding and he does fine.
I think the biggest problem with large enclosures is that BPs are pretty shy and a big enclosure can make them feel 'watched'. It can be dealt with if you get plenty of hides of the appropriate size, though. Fake plants also help.