If it was me, and it's not......I would cut a hole in the ceiling interior at least. Then put a dehumidifier on a short stepladder, or platform, so that the dehumidifier can drain into the shower as it collects moisture. Close the door of the bathroom, too. Spray a mixture of chlorine bleach and water up into there and let the dehumidifier dry out the area. If you're brave enough, get some forced ventilation similarly into the delam area from the outside or inside.
It's relatively easy to weatherproof your outside repair with those dicor sealants. There are seams everywhere on an rv, and the only ones that leak are the ones that flex, or that weren't done with the right sealant, or have been left in the sun for a long time and crack. Your access patch on the outside (or inside) wall should be pretty flex-free, and can be artfully disguised with a refrigerator plastic vent cover, or some kind of factory looking panel maybe, (non functional except to cover the repair seam).
I think water intrusion should be dried and sprayed with mold killing spray ASAP. Good for you getting the skylight fixed right away, I would start drying right away. In my experience, forcing air into hidden wet areas can make a huge difference, over days of time spent drying. I have read that mold can be made dormant but not permanently killed, by drying completely. I say treat it, dry it, then look at a 'correct' repair when you can. Meanwhile, you need to get some dry air to it.
