Extemely hard to remove stains from the tub. Don't use any harsh cleaning material. Such as AJax or other powered material. Use a liquid that is non-abrasive. Such as, Soft and Scub. Any mild form of cleaning is okay.
Soap under the mat can cause stains and actually eat away at enamel.
Only proper way to reglaze is to spray. The products generally can only be purchased thru a company by a professional applicator.
If you try to reglaze and mess up, then correcting your mistake will take a lot of time and money. Also, you will be using harmful products with strong fumes. Be careful. We use safety equipment when doing preparation and spaying.