Cuda, Please solve the mystery and let us know what car/truck/van/prototype vehicle you selected. If its something vanilla, just lie to us.
Needs a little work but would be a cool ride.... https://philadelphia.craigslist.org/cto/d/1969-chevy-van/6505357471.html
Now here is a wagon! https://southjersey.craigslist.org/cto/d/1966-dodge-monaco-9-passenger/6513205043.html
That's what I went with. $3K for a 2007 with 190K on it. 10' board right down the center with still having access to 5 seats.
I've had a few Honda Odysseys - they can take a 10'6" right down the middle with use of 4 seats. How is does the 12' glider fit inside the Sienna?
I would guess by folding the front passenger and middle passenger seats flat ( they fold completely flat) and placing the board on top of those seats and up to the windshield. There would still be access to 3 seats too.
I have been looking at Siennas, sure are a lot of them and All Wheel Drive was an option. Most have a drink holder/storage bin between the front seats that is easily removed, making more room for boards down the center