Treating a rental rehearsal room 20'x20'x18'?

Still making progress - Slowly but surely. I re-built my Drum Cloud - took down the 4' x 6' x 4" thick 703 topless cloud and replaced it with a 4' x 8' x 12" deep hard topped cloud using pink insulation (approx 5000-6000 rayls/m). I also tacked up a few 2' x 4' x 4" thick wall absorbers by the 1st reflection point on the drums (spaced 4" off the wall). A few pics below... Much more stuff to come! I'll be picking up 24 more 2" 703 panels this weekend and start on the corner super chunks and some more wall absorbers. I can already hear the Snare Drum and Kick starting to get more impact and clarity - and the cymbals sound smoother and more coherent as well - exactly what I'm after! I do have a question regarding wall absorbers. John specifically confirmed in another thread that a hard topped cloud that is angled appropriately with parallel floor/ceilings would help with my 50Hz ceiling mode issues, and a topless cloud (as I had before) would do literally nothing in the low bass range. Going by that rationale - I still have 2 parallel walls in this room. Would building some hard-backed wall-panel absorbers and attaching them at an angle be of the same benefit in the low bass region for the walls? I can't see why this would be any different from a parallel floor/ceiling with a hard-topped cloud versus a parallel set of walls with some angled hard-backed wall panels - but I'm a drummer after all :) I'd also LOVE a few confirmations on my new cloud (pics below and also in the other "My Cloud Design" thread on page 2). I built it from 1" x 12" lumber. It uses a 4' x 8' piece of 1/2" B/C plywood as the top with a single 1" x 4" brace across the middle as pictured - and is sealed tightly. Does the top need to be stiffer (thicker or more bracing) or does this sound alright? I'm pondering replacing the other 2 topless clouds with this type design for even more ceiling mode bass control - so I still have time to revise my plan and use a thicker top or more bracing... Thanks for all fo the input. This is shaping up nicely - if not slowly :)