air head

i am looking into a composting toilet. how much clearance do you have from the top of the unit to your headliner/hatch? i have a raised fiberglass “step” on which the head would be mounted and i am concerned about that the space above the head may not be sufficient. not so sure it would be a good idea or if it even possible to cut into that “step”.

how long have you used the airhead? any thoughts on airhead vs natures head? did you install a solar vent? if so, would it be possible to post a picture?

thanks for the input