I am not positive, but I believe you get it back very quickly. I wouldnt want to give out my SSN either. If you already have a EIN though then I would give them that without a problem.
I believe it has to do with import tax's which you would have to talk to someone more knowledgeable about taxes then me on if you have to pay them.
The garage costs more than $2500?
Customs border patrol requires the ultimate importer to be identified.
Do a google search on cbp importers social security number.
They have a nice explanation. Getting an ein number would protect your social if you need to go this route. If it's less than $2500 then you don't need to provide ss#