Leaving the gas-bag outside? Good luck with that. I have a bit of knowledge of yacht sails and microlights (like Ikarus C42 and Rans S6) - I wouldn't expect them to last more than a couple of years if I left them exposed to the elements in all weathers.
If you're planning to have your gas-bag 'sucked down' onto a piece of concrete then that suction has to come from somewhere and that will also add to the cost. Also, is this suction going to cope with 40kts+ of wind that's not exactly freak weather these days?
One wonders why the company has bothered with the expense of restoring Cardington if it doesn't need to protect its gas-bags from all weathers?
Oh, and as for Concorde? I think they built 20 and operated 14. I'd be staggered if HAV get a quarter of those sales!
LJ