I have a 2014 LWB that I bought for use as an occasional camper of sorts. I am 6 feet tall and I wasn't able to lay down in the rear of the short wheelbase transit connect unless I slept diagonally. I measured 5 feet 11 inches from rear door to the back of the front seats, in the long wheelbase version I had 7 feet of room)
This may not exactly apply to a SWB but I'm guessing it'll be similar.
I removed the third row seats and seat belts altogether.
In the back I put a rock climbing pad that I had because it was the same height as the 2nd row seats when folded down.
I fold only the left 60% side of the 60/40 middle row down and that allows me to fit a 6 inch twin size memory foam mattress in the back. I only had to trim about 6 inches off the mattress up neat the middle seat that is still up right. Width wise it leaves some room beside the mattress if I want to sit up. Headroom isn't an issue.
I have room on the side of the bed for a plastic storage bin that double as a night stand.
The 3rd row windows are blacked out with some fleece material from Walmart.
I then installed 4 compression curtain rods (rear window, both second row windows and between the first and second row seats) with blackout curtains.
When the bed is in place I have access to 3 seats for carrying people, when I need all 5 seats I fold the memory foam mattress in half over itself and flip up the other seat.
I have used it more than I thought I would. I normally sit in alot of traffic going to work in the morning, so now on occasion I drive to work at 10pm when I would normally be going to bed and sleep in the van in the parking lot. I wake up in the morning and enjoy a nice short commute to work The memory foam mattress combined with the rock climbing pad provides almost as much comfort as my big memory foam mattress at home and with a -30F sleeping bag it's been very toasty even with the temperatures we are getting now in December in New England.
I suppose you could say that I'm a happy camper...