It's also possible that you could continue to try removing the remaining screws. I assume you have tried a little penetrating oil on them first. If they all break off, removal of the trim ring should be easy at that point. If the screw heads are stripped, a little careful work with a grinder should finish those off. Once the trim ring is removed, there may be some remaining material that sticks out above the surface of the van side, and getting a pair of vicegrips on them may be possible. If not, drilling them out should be possible, but a little difficult to remain centered. (these will help
https://www.zoro.com/bosch-self-cent...0/#description) Or, grinding the material flat, center punching, and then drilling with a smaller drill bit at first will really help. If you can then tap in an Easy out, you should be able to back the screw out.
You will be able to re-use the old holes and you won't have extra holes to plug if you drill new ones instead.