I made a funky but servicable black plastic filler box out of ABS sheet and previously posted a pic
here .
Recently, I ordered another cheap Kenwood HU to redo my boat setup from Crutchfield. They asked "what kind of car is it going it to?" I figured, what the heck, get a spare harness adapter for my car so I told them a WRX.
Well, in addition to the harness adapter they sent a newer-style all-purpose modular black pocket that came with 3 different trim rings and two different styles of side adapter plates. The largest trim ring covers the sled flange quite well, and, with one of the 2 side plates installed, if pops in the sled opening neatly (I did snip some protrusions off the side plates and bevelled the back edge of the top of the trim ring a little.
Anyhow, a pic of the box is attached. A few in-car pics to follow. Sadly, I mislaid the plastic bag this came in so I don't know the manufacturer (will dig through the trash bucket on the boat and post if I find it), but a Crutchfield rep should be able to puzzle it out. I'd guess it couldn't cost more than $10-$15.
I may do a little more work on this to shave the back of the trim ring so that it doesn't protrude as much then lock all the plastic parts in place with some (what else?) JB Weld.
Jim