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Moved many a spa this way. Works well and is the easiest way to move a single spa (slide the cover in the bed, under the spa). Frequently you can stand the spa on edge on the ground, back the truck up to it, and tip the spa down onto the edge of the truck bed, with 2 people. Just be sure to strap it down well, and you might want to consider some padding on the top of the trucks bed to prevent damage to the paint. Also you'll want to slide the spa as far forward as possible on the truck. You don't want to hit the breaks and have the spa in the cab with you :-)
But you have lots of experience in moving spas, right?