I have the deadening material on mine, with extra strips in the troughs of the floor, but if you are looking for flatness and levelness under the carpet I think It will be difficult to get it perfect.  I would make a cardboard pattern of the floor area and transfer it to 1/4" or even thinner plywood. This would give you an underlayment for the carpet that would not create an uneven surface.  Results without it may depend on the chacterisitcs of your carpet or if you care about it that much.  Good luck!
Stephen
 

    On Friday, November 11, 2016 12:49 AM, John Rodgers <jrodgers113@GMAIL.COM> wrote:
 

 To the best of my knowledge, all the vans middle section has s type of
corrugated steel floor, and some type of fitted floors board material to
level out the floor for a smooth fitting carpet. The flooring material in
my van is not there, just the steel floor.  I think I have some spotted,
but wondered if it would me better to level the steel floor with the 3m
sound deadening material I have on hand. It's a three inch wide mastic like
tape that sticks down pretty well. I have used t in some places for sound
desdening, but this floor leveling for carpet would be different.

What think The List?

John