First off let me say, I like bondo's cap. I don't have a truck it would work on but I think on the right truck it's cool looking and I'm of the old school car mentality; cool = good.
From what i could see on that forum most of those guys had big tire, ugly, quadcab trucks. The tires alone are killing their mileage (i'm sure they are not above 20psi).
Once upon a time i worked on NASCAR Modifieds.
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These cars have 650+HP, 15" wide tires, are only 2" off the ground, and are faster than Cup cars when not restricted by plates. The general thought was the cars had the aerodynamics of bricks because of the huge tires. When the newer (mid 90's) interior panels were made the drivers figured out pretty quick that was not the case. The air was allowed to flow through the right side of the car more unrestricted than ever to the spoiler for rear downforce. Also around the same time work was done to the front spoiler to find the best downforce/drag combination.
The general mindset is still that they are not very aerodymanic. However, as it was previously mentioned form follows function and for a 150mph race car you want as much tire as possible for traction, and bodywork that produces downforce.
Those guys want to spend all their money on gas and toys, eventually they will come around, it's a testosterone thing with them.