Somebody once advised me that when taking an instrument across the border, I should first stop at the US side of Customs and get forms to certify that my instruments were purchased in the US, and date of purchase, manufacture, etc. I did that, though I haven't needed them for awhile. Once you have that form, keep it for that instrument, and you can then account for all of your instruments at the border should you ever be challenged.

I don't know if that helps with the wood issue, but it can't hurt.

Dan