You probably already saw my thread about adding a third captain's chair to my EB:
viewtopic.php?f=13&t=9212&hilit=+captain%27s+chair
We got a removable, swivel base for it. Being able to remove it is great. We haven't used the swivel function much. We also used a seatbelt with a QR function. Upper belt support was mounted to the side of the van, with a reinforcing plate behind it. The seatbase mounts to the van with four big bolts, with serious reinforcing plates under the van.
If I had it to do again, this is what I'd change:
1. Probably not go with the swivel base, as it cost more, was harder to find, and we rarely use it.
2. Look for a chair with the integrated seatbelt setup, so that we wouldn't have to mount the shoulder point to the van.
3. Find a seat that was a bit less "chunky" than our current one, which eats up a lot of space in the van. But, I guess this is just a fact of life with the aftermarket captain's chairs. I got this one on CL for $125, so can't complain too much. I've thought about swapping it out for an OEM Ford front seat, though. Plus, we're always whacking the armrest when we are walking through the van.
LATCH is a great setup, but not 100% necessary IMO. It was mainly designed to make it easier for people to correctly install their child seats, as many people just can't seem to do it right unless it's "idiot-proof." You can use a carseat just fine with a lap belt. The rear tether is a good idea, but you can also set this up using a D-ring bolted to your seatbase or someplace similar.