I do not recommend Epoxy over oil-based stains. Epoxy generally does not adhere well to oil-based stains and Minwax oil-based stains are notorious for bad adhesion.
If you have an oil-based stain on your surface, you will need to apply 2-3 coats of oil-based polyurethane before applying the epoxy coat. The polyurethane will allow the epoxy to stick.
You can use this product by Pro Marine that will do the job.