I imagine you could still make do with a smaller one, though it would mean only a few smaller-sized Pokémon could be in it at the same time as the Drampa. Unless, of course, you're quite determined to have it be as large as possible.
Though in any case I doubt filling it with Pokéballs would be very practical for a number of reasons.
Re: Text
Though in any case I doubt filling it with Pokéballs would be very practical for a number of reasons.