Yes I believe you can opt to remove your address from the electoral register but few bother. Likewise telephone directories etc.
Still, I should think the chances are slim of burglars trawling the FCA records to find an anonymous mailing address for a model club and then breaking in to that address on the off chance of nicking a few tools and or a very specialised loco that could only be sold to a very specialised buyer, or a scrap merchant.
It would be far easier for burglars to discreetly follow members home from a steaming day at the club track, after seeing what valuable loco they load into their vehicle. But how many members circle the block and check their mirrors to see if they are being followed? Exactly none would be my guess.
Mailbox at the club premises seems a good idea, provided it is kept locked to stop the credit card thieves etc from emptying it.
And so it goes on. What a world we live in.