A good supplier , or hardware store, will have "peel and sticK". It comes both in strips, ~ 1" wide, or as a complete mat, approx 12 x 24. They can get dirty, but but can be removed from a steel tub using alcohol or mineral spirits.
By the way, many years ago I had some sprained knee issues, both knees but not at the same time. In that time frame, I put up a LOT of grab bars, both inside and outside the tub. These have been a lifesaver more than once in subsequent years.