Use fed-ex, USPS are ok as well, and as long as it's packed extremely well it'll be fine. However if you are going to undervalue it, then you have to ship with a company that is good, and fedex have always been reliable and quality, plus the extra you pay, you then save with undervaluation.
I mean, you may get caught out, but it's a risk that is worth it, as I think they really charge far too much for importing, it's obscene.
Saying that, last time i got guitars, i went on holiday to the US, had them shipped to my hotel, then flew back with them, which is the easiest way really, and you get a holiday out of it!
Just avoid UPS. Any company that manages to lose 2 100lbs
speaker cabs is incompetent beyond belief.