Alister,
Yes, it does provide some 'scuff' resistance but if you want better protection you can use Poly-C instead of dope with it, (available from the same page), or a lightweight glass cloth. Looking at your build I'd say that a heavyweight tissue would be fine.
Poly-C is a water based polyurethane varnish so would still need 'sealing' before you put the varnish on to it, a couple of coats of sanding sealer is usually sufficient but I'd advise trying it out on a piece of scrap balsa the same thickness first.
Mark