Just to answer my own Q -- there's over 6 feet in the back, with the seats moved/tilted forward, even if you're *not* on a diagonal. I'm over 6 feet tall and have an inch or two to spare laying straight back.
Despite, that, I'm still going to try removing the front passenger seat for my next extended road trip. It takes up valuable space, and the unnecessary weight impairs fuel economy.
This will also allow me to keep a sleeping area permanently in place, and much easier to access when pulling over to sleep. (Just move right two feet and lie down.) On my last trip, it was a pain setting up and getting into the bed by opening the doors, getting out of the car, moving/tilting both seats forward (which meant also going around to the other side of the car, opening those doors, etc.), folding down the mattresses, awkwardly closing the front door after the rear door -- from the back -- etc.
Not stuff you want to deal with when tired and ready for bed.
And it was equally a pain getting out of the sleeping area, because you can't open the rear door without first opening the front door. Removing the front passenger seat will create a much better flow, make it easy to exit the front passenger door, make it easy to hop back in the driver's seat, etc.
In total, there will now be a 9+ foot space to stretch out and utilize (counting the footwell under the dash). And with a flat center console, almost 60% of the front area should be opened up for sleeping and storage. Will also make it possible/easier to transport longer/larger cargo.
(And as noted before, a passenger or 2 could lie comfortably in the back.)
I'll probably have a split mattress in the back, so one is always fully extended, and one can remain shorter. That way, I won't have to adjust the driver's seat before sleeping, and if I have a girl with me, they should still fit just fine (most being shorter.)
Looking forward to trying this next Spring. Will research the safety issues, and see if there's any way to dummy up the connection to fool the SRS system (and ensure it remains operational). Will keep you guys posted and post photos if/when I'm able to set this up. Will be nice to have such an open space.
