For airspace?
The recommended air space for those subs ported is 1.75 to 2.25 cubes per sub. So, for four you would need at least 7 cubes after all displacement. With your dimensions, you've only got about 8 to begin with. After the thickness of the wood, bracing, sub and port displacement you won't have near enough air space left.
For sealed it's 1 to 1.5 cubes per sub. So, you would only need 4 cubes. And sealed boxes don't have as much internal displacement as ported. Plenty of room for that.
Nah, one big box is fine.