Re: enclosure stuffing and bracing
I'm not too sure about the closed cell foam you glued to the inside of the box, seems more like it won't do anything but shouldn't hurt.
as long as you glued and screwed all the edges well on the box you shouldn't need bracing on a box that small on that little power.
I would just carpet the whole box up and then cut the holes out. Overlap the carpet under the lip of the sub right up to the edge of the hole in the wood.
Don't use staples unless you have to.
Velcro should work fine for a box of that size and weight.
Pictures of your work and the box would help also, if you took any while building.
In the process of being installed:
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