How do I cover rust on inside of window wells?

I have three egress window wells that will last for years yet, but because they are slowly rusting from the outside the rust risidue leaks into the inside and look awful. I am surprised that a "barrier" wasn't applied to the outside of the wells before they were put into place which should have kept this from happening. We bought the house when it was four years old. I had them painted one time but painting them lasted for a limited period of time. I need a product that would be relatively easy to apply that would stop the rust from bleeding through. I have thought perhaps a vinyl lining could be applied so the rust would not bleed through and show from the inside of the wells, but is there such a product available and how difficult would it be to apply? Is there a thick spray finish that would seal the holes that have have appared and prevent new rust from appearing? I need it to last for a number of years and would prefer that it could be painted, or look good enough on application that it wouldn't need to be painted? The windows are the only source of daylight and the only view from inside so I would like whatever product I could use would look reasonably good as well as do the job. . Some have suggested using bondo, but the entire inside needs to be covered to keep future rest spots from appearing where the bondo has not been applied. If it didn't work it would make a bigger problem than I already have. With all of the new products continually coming on the market there might be something that would work that I don't know about. The problem is something like rust forming on the inside of a car part and eventually eating a hole that appears on the outside (viewing side) of the area. I know that bondo is often used for these repairs, but I understand they require a lot of sanding after the bondo dries, the corregation would make sanding specific areas very difficult, and a very large ares needs to be covered in order to be effective. These are large areas that I want/need to cover.