Hi there...
Took delivery of the Defender for my Note 2 last week. One thing I forgot about when selecting the case was the car mount issue. I dont like generic ones where you have to close jaws on the device etc.
So, knowing I wont use the belt clip (it looks like a laptop on your belt) it made sense to use this in some way.
I am a huge fan of the Brodit system of pro-clips (clips that attach to your car and offer a base to mount device specific holders onto) and the associated device holders.
I already had 2 adjustable holders that I used for an iPhone with a case on and what they call the 'move clip'
Move clip: MoveClip*MoveClip Mini. 2 female + 1 male. 50 x 35 x 4 mm.*213005*|*Brodit
iPhone Adjustable holder with Tilt/Swivel: Passive holder with tilt swivel*Adjustable holder. Fits devices with skin (NOT for Apple original Bumper).*Apple*iPhone 4S*511165*|*Brodit
So, what i did, was to use a dremel and take off the clip part of the otterbox case. I realised after there was no need to be so forcefull. Under the clip are two prongs that with the right tool could be compressed and the belt clip would detach from the other half.
Once this was removed there is a raised area on the back that I sanded down using a dremel and a small sander.
When this was quite flat, I used epoxy resin to glue on part of the move clip.

IMG_0670-small by StephenT1971, on Flickr
I took the tilt/swivel part of the iphone holder off. Its in two peices, its basically a ball and socket. The moveable ball stays on the proclip. The other part, I glued the other side of the moveclip onto and drilled a hole through it so I can attach it back to the ball side.

IMG_0661-small by StephenT1971, on Flickr
This means that my new Defender mount slides on using the 'move clip'

IMG_0665-small by StephenT1971, on Flickr

IMG_0655-small by StephenT1971, on Flickr
As I will also use the D3O impact case and need a car holder for that, I modified my second iPhone holder.
The iPhone holder is adjusted in width with the thumbscrews at the back of the holder. Thats no good now as I need to put the move clip there. So used the back plate of the first holder with the back plate of the second one to clamp the adjustable sides together and aim to have the thumbscrews at the front. This means I can glue the move clip to the back in a similar fashion to the Otterbox holder.

IMG_0664-small by StephenT1971, on Flickr

IMG_0663-small by StephenT1971, on Flickr

IMG_0662-small by StephenT1971, on Flickr
So, in a matter of seconds I can swap the phone holder, dependant on what case im using
As the case is quite a tight fit in the holder, I used a heat gun on the section that holds the phone in and bent it ever so slightly so its easy to remove yet grasps it enough to keep it secure in the car.
I had to make a small cut out at the bottom of the otterbox holder so its easier to pull out the rubber port cover for the charger:

IMG_0666-small by StephenT1971, on Flickr
Here it is in use:

IMG_0658-small by StephenT1971, on Flickr

IMG_0656-small by StephenT1971, on Flickr
Took delivery of the Defender for my Note 2 last week. One thing I forgot about when selecting the case was the car mount issue. I dont like generic ones where you have to close jaws on the device etc.
So, knowing I wont use the belt clip (it looks like a laptop on your belt) it made sense to use this in some way.
I am a huge fan of the Brodit system of pro-clips (clips that attach to your car and offer a base to mount device specific holders onto) and the associated device holders.
I already had 2 adjustable holders that I used for an iPhone with a case on and what they call the 'move clip'
Move clip: MoveClip*MoveClip Mini. 2 female + 1 male. 50 x 35 x 4 mm.*213005*|*Brodit
iPhone Adjustable holder with Tilt/Swivel: Passive holder with tilt swivel*Adjustable holder. Fits devices with skin (NOT for Apple original Bumper).*Apple*iPhone 4S*511165*|*Brodit
So, what i did, was to use a dremel and take off the clip part of the otterbox case. I realised after there was no need to be so forcefull. Under the clip are two prongs that with the right tool could be compressed and the belt clip would detach from the other half.
Once this was removed there is a raised area on the back that I sanded down using a dremel and a small sander.
When this was quite flat, I used epoxy resin to glue on part of the move clip.

IMG_0670-small by StephenT1971, on Flickr
I took the tilt/swivel part of the iphone holder off. Its in two peices, its basically a ball and socket. The moveable ball stays on the proclip. The other part, I glued the other side of the moveclip onto and drilled a hole through it so I can attach it back to the ball side.

IMG_0661-small by StephenT1971, on Flickr
This means that my new Defender mount slides on using the 'move clip'

IMG_0665-small by StephenT1971, on Flickr

IMG_0655-small by StephenT1971, on Flickr
As I will also use the D3O impact case and need a car holder for that, I modified my second iPhone holder.
The iPhone holder is adjusted in width with the thumbscrews at the back of the holder. Thats no good now as I need to put the move clip there. So used the back plate of the first holder with the back plate of the second one to clamp the adjustable sides together and aim to have the thumbscrews at the front. This means I can glue the move clip to the back in a similar fashion to the Otterbox holder.

IMG_0664-small by StephenT1971, on Flickr

IMG_0663-small by StephenT1971, on Flickr

IMG_0662-small by StephenT1971, on Flickr
So, in a matter of seconds I can swap the phone holder, dependant on what case im using

As the case is quite a tight fit in the holder, I used a heat gun on the section that holds the phone in and bent it ever so slightly so its easy to remove yet grasps it enough to keep it secure in the car.
I had to make a small cut out at the bottom of the otterbox holder so its easier to pull out the rubber port cover for the charger:

IMG_0666-small by StephenT1971, on Flickr
Here it is in use:

IMG_0658-small by StephenT1971, on Flickr

IMG_0656-small by StephenT1971, on Flickr