Doom cubes exploit many mechanics in the game, because most of them are based on dimensions. Turning is probably the worst balanced value currently out there.
I one made a death ship with no smooth edges. I did, however, add a kind of interior, and I got really creative with the exits once. I made the central part out of ice crystals, and then made 3x3 doors in each side of the cube (the central part was a cube), and then I put something that looked like a table above each exit for protection. The end result was quite nice.
Later versions had lots of black hardened hull, with a very bright interior and a periscope like structur on the one end, which basically was used to cover the entrance and the camera I needed for my salvage ship (it had quite good shielding and weapons too).
Conclusion: people should be allowed to create death cubes if they make an effort to have a nicely styled exterior or interior, or both of course.