SAFE DEPOSIT BOXES ARE NOT SAFE. THEY OFTEN GET DRILLED.

IF YOU MUST USE A SAFE DEPOSIT BOX KEEP A COLDCARD IN THERE RATHER THAN STEEL PLATE SO IT IS PROTECTED BY A PIN AT LEAST.

OR USE A PASSPHRASE. OR USE MULTISIG.

BUT IN ALL SITUATIONS ASSUME THE SAFE DEPOSIT BOX WILL BE COMPROMISED AND MITIGATE THAT RISK.

AS FOR TRUST SETUP, I LIKE MULTISIG BEST. GIVES YOU A LOT OF FLEXIBILITY. 

EX: YOU HOLD TWO KEYS, HEIR HOLDS ONE, LAWYER HOLDS ONE - HEIR AND LAWYER WOULD HAVE TO COLLUDE TO SPEND FUNDS - IF BOTH LOSE KEYS YOU CAN STILL MOVE FUNDS. 

 Suggestions on multisig?

How about splitting the seed into two safe deposit boxes as different institutions?