[Big Dave]

It does look a bit like a fugitive from the IKEA website...

Fender skirt in your case indeed won't cover the wheels/tires, but would fair off the "parachute" aspect of the wheel wells. Pizza-pan wheel covers?

Don't get too fancy on this version. drive it and get a feel for it and see how much it helps your MPG. Like my old rubber apparition, you seem to have no lid and have made your truck into a 2x4 carrier. You'll eventually get around to thinking about a lid.

Your plywood and lumber lid should last a year or two. Long enough to think about the beta. The guy that got my rubber apparition is still using it. That thing is six years old now. I built it to last six weeks.