Relocating Internationally with Large LEGO Collection

Can anyone who has relocated internationally with a large LEGO collection share their experiences and advice? New unopened sets are a specific concern. We're told they're likely to be taxed if customs inspects them? It's possible to dispute if we have still have the old invoices. But it's probably easier to just sell now and re-buy later. Sadly it's alot of hassle especially for older rare sets. Anyone successfully explained that unopened boxes are a collector's quirk? Otherwise for opened...