Yeah well thats what i had done in my 350, I had gotten in an under strut bar box from america which housed 2 10" subs and i had the amp hidden behind the passenger seat in the compartment. I was really happy with that setup... until the 370 came out lol
I emailed zenclosures about the box but i got a wacky price back for shipping, he said like $550 just delivery, he may just not be interested in overseas shipping, as the box i got for the 350, cost me only about $75 and it was the same size if not bigger.
Its a real bummer too because zenclosures have a nice upward firing box for the 370 which could mount an amp facing the hatch... would be perfect