disclaimer: follow the manufacturers recommendation.
reality: i have the 5360 mounted under a table 6" on left. 12" rear, right open, 20" above..no issues at all. Your cabinet is much more confined tho.
5360 draws air in from 3 sides, and exhausts it out the front, 45 deg away from lens. It should be ok IF you can make sure only cool air is being drawn in. Maybe open the back of the cabinet etc. The fan doesn't move a lot of air - if the stagnant air is recirculated, it could shorten bulb life.
That said, people use these projectors in 100+ temps, and whether the bulb lasts 2000hrs or 5000 is still pretty random. As long as you can ensure clean, cool air is being drawn into the projector...i think it will be fine.