After the car wash scene the uniforms were wet.
Minutes later, they were dry.
When the crooks drive away from the cops in the final scene, the car loudly "peels rubber" from the spinning rear tires on the non-paved dirt road.
Gomer and Duke have set up a roadblock, looking for smugglers. An older woman is stopped and Gomer comments on her loose fan belt, etc. She asks him to check the oil and coolant while he's there. He takes off the radiator cap. It's not locked, probably because of multiple takes, and Gomer would never just remove the cap, as he'd risk being scalded.
Gomer is wearing his fatigue shirt with hidden pocket buttons and the USMC emblem printed on his left pocket. Duke is wearing a fatigue shirt, but the pocket style is different, the buttons are visible, and there is no USMC emblem printed on the left pocket. Dukes shirt is possibly from the Army or USAF as they used that type of design.
When Mr Burton is wearing Gomer's uniform, the shirt is slightly olive-green, but when Gomer was wearing it, it was the expected tan which matches his pants.