curious as to why your getting 3 x 150w HPS's in there... that's 450w total, why not just get 1 x 400w HPS in a cool tube, save space and money a 400w in a cool tube with an inline fan will probs cost you around £180 roughly $200 or so (my conversion is wack), that's what I'm doing and by the looks of it my cab is roughly the same size as yours check it out in my sig. I'm confident that I can control temps in it and I'm going to do ScrOG.
Actually looking at it your space is way bigger than mine XD
My recommendation would be to go with the 400w HPS in a cool tube and mount it along the depth so that the extraction is out the back and do a dished ScrOG... I don't know how better to describe how to put the light, something like this:
_________________ (top of cab front on view)
|-----------O-----------| (Light)
ignore the dashes XD