Nope, sorry, you have completely missed the point! The Polyspan, silk, japanese tissue, or silkspan is attached only around the periphery, then the SLC (super light covering, a vey thin Mylar with adhesive coating) is applied OVER it and heat bonded to the fiber underlayer. The fiber layer, whatever it is, is NOT DOPED IN THE OPEN BAYS. The SLC provides both the function of filler, binding film and fuel proofing even if no other finish is applied.
The result is a composite covering that is incredibly light, tough and rigid, but fuel proof or paint ready without multiple layers of dope and filler.
This way of covering is exactly reversed from your standard practice of covering with SLC then applying one of the fiber coverings doped over it. Yes that works, but you still have to then apply dope to fill the fiber and fuelproof it. Putting the SLC on top of the raw fiber gives you the same strength with a LOT less work, time and weight. Also, IMHO a better finish than I have the patience to achieve otherwise.
As mentioned elsewhere, with Polyspan, the result weighs. only 1.4 ounces per sq.yard.