G'day Paul,

Yes the Darche KOZI Queen mattress would be the best fit in the Nebula 1550 Swag as it is pretty close to the sleeping area size, looks like that would be the one Mad Matt is using.

G'day Lauren,

The dimensions are for the box it is delivered in. The mat is pretty snug in the box. I would still budget for that type of space in your car though. At the moment it is rolled up probably the tightest is can get and after the first use it is not likely to get that tight again.

G'day Meredith,

The Oztrail Fatmat is 15cm thick so isnt really comparable in terms of comfort with the Zempire Monstamat or the Kozi Queen, as they're both 10cm.
Whilst comfort is very subjective, I personally find the Kozi Queen to be a bit firmer than the Monstamat.  I have slept on one several times at a friends place without any issues, but I found the Monstamat better suited to my comfort.
Its probably worth mentioning that another person may have a completely different opinion, so in this situations its great to read the product reviews from customers - often this extra info can be the deciding factor.

G'day Caity,

Yep, absolutely.  As long as the dimensions of the mattress line up with the dimensions of your swag, it is a bonded mat which means there won't be any issues storing it rolled up inside.
We'd recommend you inflate the mattress at least once every 3months or so if you're not heading away regularly.

G'day Jackson,

It won't sorry, this mattress is 148cm wide where as the swag is 140cm wide.
You're better off going with the double mat option, check it out here.

G'day Scott,

Yes, that's correct, but manually pumping air into a bonded self-inflating mattress can cause the fabric to separate from the foam.
Any extra air should be added with caution.

G'day James,

There's no R-Value on these mattresses as Darche have yet to test them.
I'm not sure if its something they're planning to do in the future, as their All Terrain Mat also hasn't undergone ASTM testing.

G'day Imran,

The differences really come down to the materials and valves.
The All Terrain Mattress is a much more heavy-duty option, with PVC outer and larger heavy-duty valves.  Its designed to go its swags and for more rugged adventures.
The Kozi is great family camping mattress option aimed more for car camping - tents and stretchers.  It has a softer stretchy outer fabric, so comfortable to sleep on without a sheet, etc and a slightly softer internal foam, with a much smaller pack size.

G'day Rachel,

They're semi bonded, so will be fine to store rolled up.

G'day Rachel,

Generally, it is best practice to store a fully bonded mat in the unrolled position with the valves open, however, reality dictates this isn't always possible, and the majority of all self-inflating mats will be stored rolled up. A semi-bonded mat is less likely to have ongoing issues if stored rolled up as Lauren suggested. 
If you're not able to store it unrolled, then popping it out and letting it inflate, then packing it away once a quarter will be just as effective.