It's funny.... I feel like I am in the same boat you were, building essentially the same van... staring at a pile of parts and a pair of axles in the garage waiting for the weather and the time to start tearing into it.  
I look forward to seeing how you go about building the interior.  I too would like to be able to reconfigure the layout and was thinking about l-track.  I haven't yet convinced myself if its strong enough to mount seats, but I want to.  
Any plans for a house battery and/or a furnace?