We have been looking into similar options.
One thing to consider about your rear seat, is headrests, or higher backed seats, not an issue when using a reverse facing seat, but once the kids are in front facing boosters, the headrests/high backs provide much better support for the car seats.
The problem with the D-ring or similar option is that even with grade 8 hardware, you are still only bolting it to thin sheetmetal. So to do it right would need some type of welded reinforcement underneath that can be bolted through.
My current plan is to use a newer OEM seat...either 2 buckets or a 3rd row bench that already are built with "LATCH Lower Anchors" (the little metal loops between seat and backrest you clip car seats into on modern cars), Then properly bolt and secure the seat down...maybe with a little overkill reinforcement.
Of course with the oem seat, I'll have to have it re-upholstered to match other seats, but thats not a big deal.
Also, make sure you have top notch seatbelts from a reputable manufacturer. Not a place I'd choose to go with surplus or JunkYard pulls.
In my mind, this is the one area that no expense should be spared. Especially considering EB's are missing practically every other standard safety feature of a modern vehicle.
