@sdnative, the interior dimensions are 90" x 50". Pretty large by mat standards, so the megamat duo will fit fine.
This summer I bought (and very shortly after, sold) an AluCab Gen3 RTT. The primary reason for selling was the small interior width. Coming in at around the same 50-51" wide, it was simply impossible for the two of us to get comfortable. No room to place hands anywhere, stretch out, etc.
If you haven't had a tent that narrow before, I suggest trying to come up with a space of that same size, and spending a few nights sleeping in it. Vertical side walls and all.
By comparison, the 60" wide FSR M60 Adventure tent we had earlier was a luxurious palace; huge difference in comfort.