Not useless. Remember I plan to not engage the horde while sitting on this massive thing. They will therefore slowly and surely destroy it as they will be able to smack on it for the entire night (6 game hours on my server) with no player intervention. Hence a lot of the cube will certainly be destroyed. Therefore it's 1000 blocks in a solid cube formation to ensure enough of it is not destroyed, and thus guaranteeing it will not collapse under us.
My other thought would be a square pyramid, pointed at the top and 45 degree ramps making up all 4 sides. I'd be inside it, access via a tunnel from underground to a hatch some distance away. Again, I will not be engaging them. I've never seen them dig down on a 45 degree slope before, however all my previous pyramids have had an opening tunnel on one side to funnel them into a long kill corridor inside the pyramid, so I am not 100% sure of this idea working.
Sorry but are you claiming this would work for a day 300 horde on highest difficulty? I doubt it personally, and that is what we'll be playing. With many many thousands of hours under our belt with this game we do really know exactly what we are doing. We simply have never tried a run where we deliberately did not NOT wipe out the entire horde every bloodmoon up to highest gamestage possible, that's the new part of the planned experience.
Sounds great but way more elaborate for what I am looking for. I mean if I wanted to destroy the horde, I know right now exactly what to build, but it would be a major construction project that we simply won't have the time to invest in this time round.