We have a 150 van with a 130" wheelbase and a medium roof . It came with seating for 7. The rear two passenger seats are spaced so their is really have very little legroom. I removed both seats and pulled up the floor to see what could be done.
The seat brackets for the OEM seats are one piece for both seats. They could be moved toward the rear to free up some space behind the front driver and passenger seats, but that is all. The second row passengers have better have short legs.
I opted for changing seats. I looked at captions chairs, but they are all bulky and very expensive. I felt I needed only seating for two behind the front cab seats. I wanted the seats to swivel 360 degrees and slide.
I was able to find a shop that converted vans and buses for use with wheelchairs. They know how to install L-Track/Airline Track. I was referred to the business that sold these medical vans and they had dozens of new individual bus seats they had removed from bus conversions. I bought two 19" seats for under $200 each.
I went a little overboard in installing the L-Track, because I put in 4 100" tracks. I could have installed 25" tracks and had plenty of adjustment space for the seats.
I am very happy with the result. I now have two seats that swivel and slide. I find the 19" seats are very comfortable for traveling. The fabric is commercial grade and easy to clean. I love the option of being able to quickly adjust the seats fore and aft.
By installed 100" L-Track, the seats can be moved completely to the back of the van in anyplace in-between. Two more seats could be quickly added behind the first row. There is enough space that passengers can move between the first row seats to reach the seats behind. Two seats can be rotated to face two seats further back. A table could be installed and so on.
Finally, if I really feel I want and can afford the Captains Chairs in the future I can find ones that will fit the present Tracks.
Here is one picture. I have more on Dropbox. Unfortunately this forum feels they are have too many pixels. Here is the URL for the Dropbox.