Enclosure Covering

Try Rustoleum textured black spray paint.  It's $6 and some change per can and you'll need at least 4 coats, but it makes an easy, good-looking finish.  I painted my home speakers with it.  And on MDF, especially edges, you'll need to first apply a few coats of primer.  Sanding between finishes is not required with this paint.

If you used PVC for ports and they're still white on the inside, try this:  place the nozzle of your shop vac near one end of the port tube and spray flat black paint 12" from the other end.  The spray will flow through the tube and paint it black without drips.

Okay, this is from experience.  The MDF has two types of surfaces:  the ultra-smooth flat side and the edge.  The edge of a 3/4" sheet of MDF is the 3/4" part of it.  It is porous, and soaks up paint.  If this edge is not sealed to the degree that the flat surfaces are sealed, the difference will show when paint is applied.  Instead of a blemish-free result, you would see the unfinished edges of the MDF through the paint.

Look at the left side.  You can see the edge of the MDF because I didn't get it sealed well enough.  It's tough to see with a cheap camera and a few kilobytes, but you should still be able to discern a line running down along the left side.  That shows how the paint "took" differently on the edge compared to the finished side.  Some of that is also glue that was sanded down.  The point, though, is that any irregular surface (MDF edge or glue residue) has to be treated with a sealer, or primed more, than the majority of the enclosure.