Ddavid,
If you are driving you need to do one extra step. BEFORE you leave the US, You MUST stop at US Customs and fill out a Customs form 4455. This is a registration form and will prove that you had these firearms when you left the country. Your best bet (if driving) is to call US Customs (360-332-8661) and find out all the little details. Your valuable guns can and will be seized if you do not do this properly.
Whoever said there is no such thing as a stupid question has never worked in Law Enforcement.