Box for truck

[Joe X]

So here is a suggestion, power: to sub(s) rated, amp subsonic filter to 28Hz, minimum port clearance 4 3/4", figure is just an assembly guide, bracing is 1 1/4" wooden dowel rods:

NOTE: slightly changed dims and port style but it can be redone, I would test your single HDC3 box firing everything up just to see how it does.