In HGV driving, especially if you run into the evening/night Id never ever work on a fixed salary (unless it was so good to turn down i.e 50k). Accidents, closures, waits at sites/depots/DC no chance.
I went for an interview a couple of years ago at DX. Guy was nice, it sounded ok, we then discussed salary. It was fixed salary, £28k. I laughed and said, interview over mate. He said they paid the same £28k for HGV, 7.5t, van drivers, as they work harder so deserve the same!