Elixer only refers to the electrical center itself, not to the outside compartment door you're needing to replace (if I'm understanding your post). Try searching for RV compartment doors or something similar. There should be lots of options available.
The only caution I'd have about enlarging the hole is to make sure there's no structural members in the way of the enlargement. Since the other side has a larger door, it's not unreasonable to think that maybe there would be no structure on this side in the same areas...but it's hard to be sure without checking.