If I were going with that design, I would go for making it more simple, lighter and using less wood where it gives little benefit. Asking what each piece does make help.
What do the three horizontals at the top do? They keep the outside horizontals from bowing in or twisting but one will do as well as three, so leave out two?
At the corners is where the weight rests and two 2X4 screwed/glued at an angle will hold a truck! So the inner 2X is there only to hold the top rail from sliding off the uprights, so ask what it takes to move the top rail sideways? If there is a plywood skin added outside the joint between the top rail and uprights, how can the two move apart without tearing the plywood? If one wanted to make it more solid while we get the plywood placed, a single spike driven at an angle down at the corner and into the legs will certainly make it stay while we add the plywood and then glue will be plenty to meld the two into one solid item. To assure the wood at the end doesn't spilt as we drive the spike in, drill a hole almost the size of the spike first. It's only there as a temporary pin and will not back out once the plywood is added over the head.
Racking? With four 2X angles and plywood added on top of that? Racking is not going to happen!