Perry,
Are you using dope as the undercoat/adhesive or Rustoleum 2X? Most have advised using nitrate dope to adhere and fill. I am doing a Barnstormer and at the point of covering the wing trying to make the decision about what to cover with. You indicated that with the iron @ 300 you could heat form around the wing tip, was this part of the main wing covering or separate? Polyspan is suppose to take less dope to fill than silk or silkspan and therefore less weight. What are you planning on using to fill with?
Best, DennisT