I'm plannining on installing a Big Maxx 50k unit in my garage. There is a little cubby in the corner (18" deep x 55 wide") of my garage where I'd like to install it and have it pointed out towards garage at a 45. There is living space above garage so I'm going to horizontal vent it out the back wall. My trusses are 24" on center with the 1st one 16" from the side wall. See diagram. The ceiling is finished sheet rocked and taped. I was thinking I'd mount a 4x4 sheet of 3/4" plywood and lag bolt that to the truss. Then either mount unistrut to the plywood or directly bolt the heater to the plywood? Thoughts?