[lunarhighway]

perhaps these woven plastic covers might have some use to create certain parts of an underbody. a light frame covered with tight strong fabric could provide a smoother surface than whatevers there now.

untill the beginning of WW2 many fighter planes like the british hawaker hurricane where at least partly constructed with fabric covered frames. mostely aft fuselages and controle surfaces. aereas that must have been subjected to considderable aerodynamic force.

so it's very possible to create a light strong and aerodynamic structure using fabric like materials.
i think the key would be to have a lot of lenghtwise ribs so the distance that needs to be spanned isn't to great.