You don't have to cut up (much) of the floor. You could just mount the
rails over top of the floor. I chose not to do that.

Installing the rails is pretty straight forward. When I did it, I went
and got 2 short rails, rather than the standard long and short, as I
only planned on the single middle seat for my Westy.

Depending on your plans....You'll need the rails, and there is a metal
bracket that the screw bolts through for the rail. That bracket (at
least one on each rail...for the 2 person middle seat you probably
should get 2 per rail) is also where the bolts of the seats thread
into. Some folks don't bother to install the bolts. They just slide the
seat on and off.

You'll also need the bolts that go through that bracket and into the
bolt holes in the frame. If you are mounting on top of the floor the
OEM bolts won't be long enough, but you should be able to get metric
bolts from Lowe's.

In the original (manufacturer) install, the metal strip at the edge of
the sliding door, is in 3 pieces, rather than one.

I can take pictures of the job I did on my Westy. It isn't as neat and
clean as an original install, but it is functional and not bad looking.