Often I read that people are looking for a case for the DSATX, and I was in the same situation now. So I decided to help some of you guys out with that problem.
I didn't make pictures of the steps, but I think the pictures of the completed case will be enough to see the general idea.
For this solution you will need to remove the connector from the 20 pin cable, so you can fit all cables through the holes. Unless of course, you decide to cut a big enough hole, so that the connector fits through.
A guide how to remove the pins from the connector can be found here: http://www.youtube.com/watch?v=kXMwCQ9fIVM

Parts/Tools needed:
- Hammond Electronics 1455N1201BK case ($20-30)
- Cone-Drill
- Plastic edge protection for drilled holes
- 4 motherboard mounting screw nuts plus 4 screws that fit in those
- Drill to make mounting holes for the mounting screw nuts
- Thread cutter for the mounting screw nuts
- Dremel or similar to remove the overhanging screws and optionally cut air vents
- Optional 80 mm fan (15 mm height)
- Optional 80 mm fan dust filter or grille
- Optional 76 mm drill
- Optional rubber buffers for PC case fans or fitting screws

First off you will need to get a case. It took me quite a while to find one that is not too big and not too small. I eventually found the Hammond Electronics 1455N1201BK. I checked Google and it should be available from many different sources internationally. The bulky edges look a bit silly, but you can actually remove them. They are only a plastic frame.

After that you will need to take out the sled on which you will be able to mount your DSATX. You can also use the other side of the case to mount the PSU, but I chose to take the sled.
Now you will need to drill holes to mount your DSATX. I don't know if those nuts are the same size everywhere, so you will need to measure them yourself.
Put your DSATX on the sled and mark the mounting hole spots with a pen.

Now drill those holes (be sure to not make them to big, since you will still need to cut threads), then cut the threads accordingly.
Now you can put in the nuts. The clearance at the edge of the sled will be very tight, but you can grind a little off of the edge where the nuts will be mounted. Don't overtighten the nuts, because the case is made out of soft aluminum. You can then remove the overhanging screws on the back of the sled, by using a Dremel with a cutting disc or whatever grinder you can find. You can also leave them, if you plan on putting rubber stands there, or other mounts, etc.

Now you can drill the holes needed for the cables with your cone drill or normal metal drill.
First make the big one where the 20 pin, 4 pin, mainboard switch cable and other optional cables will fit through. I chose to also put a remote signal cable and a USB cable through for the interface. In that case I went with a 16 mm diameter hole, which also takes into account the space the edge protection takes away. I made the hole in the upper edge, right where the 20 pin connector would be, when the DSATX is in the case. After youre done with the hole, get a long enough edge protection and put it in, so the cables wont be damaged from the sharp metal edges.

You now need the 3 holes for the power cables. Fasten the DSATX on the sled and slide it in the case. Now hold one of the side plates on to where the connectors are, secure the lower edge of the plate to the sled with some tape and remove the case again. You will now have the sled connected to the plate with tape and you can easily see where to make the holes. Mark the holes and I suggest connecting these marks with a line, so they will be aligned well to each other, remove the tape and drill them (I used a 7.5 mm drill, 7 mm will work too, but I used different cable connectors, which were too wide for 7 mm). Check if the holes align well with the connectors on the DSATX.

The following parts are optional. I decided its better to do this, because else the case would be pretty much airtight and even at low load this might pose a problem sooner or later.

Find the middle of the case and use the 76 mm drill to make a hole for an 80 mm fan. Be sure to have proper fastening to the case when you do this, because in my case the drill got stuck when it was almost through and threw the case through half of the room and scratched it pretty badly, not to mention my fingers. Smoothen the edges with a fine file or sandpaper.

The case needs additional venting, so the warm air can escape. I cut 3 openings from the inside at the side of the case on each side. Be sure to buy enough cutting discs for your Dremel for this, because in my case it ate almost 2 of them. The inside fins in the case will offer enough support to make the openings more or less straight. Again smoothen the edges with a fine file or sand paper.

Now you will need to mount that 80 mm fan. I used rubber buffers to minimize vibration, cut them to a disc and simply glued them to the fan and the case.
Put on your dust filter. Either by cutting additional holes for the screws, or using a filter that supplies a magnetic sticker and will stick to that, like I did.
Connect all cables and put everything together. Done.

Additionally you can press the rail where the sled goes in a little together, because I found it has quite some clearance, causing some noise. Just use some pliers for that, but be careful not to use too much force, else the sled wont fit in anymore.

Of course all these step can be made more properly and better looking, if you have better tools than I do. I didn't care so much for looks, since it wont be visible in the car anyway, unless you look under the seat.

Pictures:
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The finished case.

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Filed off screws on the bottom with a Dremel (sorry for the bad quality).

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Front plate with the main hole for the 20 and 4 pin cables, plus the power connector holes. The white thing in the hole is the edge protector.

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This is the dust filter. It comes with a magnetic sticker ring and then just holds onto it with magnets.

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Here you can see the vent openings and the installed fan.