With polyspan, it will get tight as can be with heating and no dope. Ironing the film over it only tightens it more. YOU DON'T NEED THE WEIGHT OF DOPE! That is the whole point of this technique. A high gloss, lightweight, ultra tough finish. What elsese could you want?
I bet that if you rubbed out and waxed a film finish, it could pass as painted.
You want to suffer? Silkspan, dope, filler, silver undercoat, primer, color, top clear and rub like heck. Or spend your time practicing FLYING! Has any 20 point plane ever won the Nationals? Top 5, yes, but won?
You have to define your priorities. For anyone below the top 5 at the Nats, a film finish is ulikely to be the decider.