Ive done several big rigs over the years and while they are sometimes fun to work on, they are in no way, shape, or form easy. Like Mr Clean said, there is alot of real estate and its easy to get overwhelmed and over look things. The truth is these trucks are on the road ALL THE TIME. Most of them get very little down time, the drivers practically live in them (think about what your closet would smell like with 2 weeks worth of your dirty socks in it). Add that to the fact that 80% of these trucks are lucky to even have regular washes, let alone polishing and wax. Thankfully, Owner Opertaors seem to take alot better car of their trucks and they will be the ones giving you the most business. As for what you should charge, no two semis are the same and you cant give a flat rate for them. Hourly is really the only way to do it and come out ahead. If your looking at doing a full blown show stopper detail, count on a few days worth of work. I would definatly find out what the customers expectations are for it because throwing a number like that at a customer is sometimes a deal breaker. Basically find out if the owner is looking for a $200 job or a $2000 job.