I've discovered the Anderson Ultimate has two methods/models for attaching to the truck. One that attaches to the fifth wheel above bed mount rails and another that attaches to an underbed gooseneck attached goose ball. The latter giving you full bed access without rails sticking up.

You'll need to purchase and install the rails or gooseneck mounts separately; ~ $479.00.

FWIW, weighing in at 55lbs is the PullRite - same idea as the Anderson but costs less. Take a look at Walmart!

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I make no recommendations. I too am trying to figure all this out and this is how far I've gotten. Today I learned the mount from eTrailer takes 1-2 months to get, though you can find them at CarID or even EPAY with much shorter (and free) deliveries.