Round H-frame doing double duty as a diffuser?

Hello-
I am looking for advice/opinions on the feasibility of the following:
I am looking at putting together a 4 sub system using 2 AE dipole 18's and 2 CSS sdx12's in sealed cabinets. I plan to use dsp and 4 channels of amplification- not sure yet if I will go all mono or stereo. In any case, due to the configuration of the room, I originally planned to make h-frames for each of the dipole 18's, however, further thinking has me wondering if I might put them each in a sonotube mounted vertically facing downward, sort of a vertical round h-frame. This way, I could get the recommended 3' of space from the rear of the drivers to the nearest wall (ceiling in this case) and perhaps position them behind my Acoustat 6600's to use as a diffuser of sorts. Since I intend to cross them over at around 80Hz, I wouldn't have any resonance issues with a sonotube that was say, 3' tall. I could also perhaps put a slot on the bottom to make them into a slob of sorts....Any issues with this I am not thinking of???