All assembled.

All trimmed up!

I use Rage Xtreme body filler. The name is so manly. I find it sands a bit easier than normal Bondo. I apply to the seams liberally.

Bit of sanding later, and we're looking good. I like having as flat as possible before beginning using the router. Having a perfectly flat edge for the bearing to ride on makes the cuts more smooth.

1/2" roundover is up first on the vertical edges.

3 passes later, and we're done. That top seam will need a bit more filler later.

Hit the top edges with a chamfer bit. Some more body filler where it needs it and sanding, and we're ready for the 1st coat of primer.

I always use shellac alcohol based primer for MDF. It evaporates really quickly, so it doesn't swell the wood, and it dries really hard, which is great for sealing. I shot it out of a HVLP gun. It's a bit of a pain to clean, so I have a cheap Harbor Freight gun specifically for primer.

And here is the curse of MDF, the fuzzies!

Everything leveled out. As you can see, there is some wood exposed again, so it will need more primer. Hopefully the wood is now sealed however, and there will be no raised "fuzzies". Did some spot touchup with body filler again.

HVLP'ed some high build poly primer. Looks fairly nice and even.

Edges nice and smooth now.

Shot some matte white automotive acrylic enamel. This picture is the cabinet still wet.

Here is the rear with the paint semi dry. It will get even flatter when it is completely dry.

Pretty much all done! They have to be transported, so I'll be pulling the drivers out before moving. I only fastened with 2 screws each for audition/break in purposes. Sounds great thus far.
