When I was still ringing in on someone else's timeclock, the employer used to give a 50 dollar a month prizes for several of the best appearing trucks (later it was 100 bucks). That encouraged the guys to wash their truck, armor-all the tires, keep the trash out, wash the dash, vacuum, etc. I've got to say that they developed a culture of "keep your truck clean and neat" by giving out the 50 dollar monthly prizes. Many guys even fixed scratches and nicks on the weekend on their own time to try to get the 50 bucks. There was the occasional few who didn't really give a crap how their truck looked. Mind you, this was a company with over 100 trucks on the road, but I suspect that it would work for small operators too.