We parked there last year for the playoff final. Was spot on. Very friendly, big bar area, outdoor seating and BBQ. Very fair prices too. Easy walk to station for direct train to Wembley park. No stress - just re-booked.
It hasn't sold out. There will be plenty more available at 10am on 3rd July when those who haven't renewed, or those who moved seats will have their old seats made available. Would expect 500-1000 to to be released - just start queueing at around 9:15am to make sure you get yours!