A perfect description of my floor!  So, off with the silver rail to see
what's below (still hard to imagine that there's actually a below below
where I already am).

"I'd be surprised if the threaded inserts are missing from the floor on
the camper -- they are there on my kombi, and I just bolted in the rails
from another van (actually, I got the seat and rails from an '82 Westy
-- kinda odd...).

The bolts (and the plastic plugs) are accessible from above, but the
real flooring is corrugated metal.  If you're not down to the
body-colored metal floor, you're not down far enough.  I think by '87,
the campers typically had that raised-square-patterned vinyl flooring --
you'll need to go past this.

On most Vangons, there is another layer of formed foam-padding below the
carpet -- it has a pattern molded into it to fit the corrugations in the
floorboards.  

I don't know if the standard middle two-person seat from a 7-seat van
will fit in a camper with the refrigerator in place -- the one I pulled
this seat from had the refrigerator removed at the time.  It looks
promising, though. My seat is 46" wide, and the space between the
refrigerator and the closed door (on an '80 Westy) is about 48" -- so it
might *just* clear."