How much would it cost to ship a pallet of personal effects from San Francisco, USA to Madrid, Spain. Say, about 300 pounds/140 kilos. I don't care how long it takes - I just want to get some stuff there. What is the cheapest way to get stuff there?
Have you tried using bungee cords? they are large cords that can stretch across whatever you are trying to hold down in transit to where you are going.
if they are standard wooden pallets going inside a van, then shrink wrap should hold the contents of the pallet together fairly well. If this has to go on an open deck truck like a flatbed or step-deck, then you can use cardboard siding with metal banding and shrink wrap, and request a drop tarp to cover the pallet(s) to help preserve the shrink wrapping.
