His subs are designed to be mounted that way.would be pretty cool to pull off to be honest... it it's done right there's no reason not to do it! good luck!
only problem with that is that most subs sound awful without an enclosure... basically that is creating a free air sub... which 99% of subs do not like. the specs on subs will tell you how much airspace each sub wants, and it's typically between 1 cu.ft. for a sealed box to 5 cu.ft. for a ported box... regardless, if the sub isn't designed to work in a free air environment, it will not last, nor will it sound right.