Here is my version. A metal channel holds the wheels straight. The uprights that keep the bikes from tipping over can be bolted flat when not in use so that the rack can be folded up. As Captn.Ken said use good ratchet straps. Another thing I found was that the large pins holding the rack flat have play in their holes allowing the rack to bounce. I made two u-bolts that hold the rack tight to the bumper. Also an xx-large BBQ cover from amazon keeps them clean and dry. Safe travels.
2013 GMC Sierra 2500HD 6.0 Vortec
2014 Surveyor Sport SP220RBS