Payment Module dependent upon Order Total

[cornishpirate]

I'm trying to make an Order Total module enabled or not depending on the Order Total. Yes - I know that's odd, but I need a special case of 'No Payment Required' when an Order Total is zero due to use of Gift Vouchers or Coupons.

 

I'm struggling to achieve an expression like:

 

$this->enabled = (($order->$ordertotal > 0) ? true : false);

 

Just can't see how to get at the Order Total as soon as all data required to calculate it is available.