I can confirm 'DiGdUb' post. I had to deposit my 2x extender with them. Was bringing in 70-200mm. They say other bring in 300mm, so can use 2x extender for 600mm. Got it back when i left Open House premises.
guess some misinterpretation..
i kena some mp who interpret the rule to mean "no tc of any sort allowed, period".
brought a 1.4x, and my max range was 300mm.
the tc went into safety deposit until i exited the grounds.