Be careful. Most of what you find when you google RV skylight are replacement outer domes.
You need a complete kit that includes inner dome, garnish, outer dome, plus screws. In addition, butye tape or innersealant (use sealant recommend by manufacturer, DICOR was not recommend for my install-outgas from sealant could have fogged the plastic), outer sealant and eternabond tape for last lasyer of outer sealing.
RV Skylights, Outer, Clear Inner Dome Skylight, White Inner Garnish
Our camper had hail damage so we replaced both the inner and outer domes. We kept and used the original garnish since it matched the other garnishes in color. In case you don't know, garnish is the trim around the inner dome that covers edges up and masks the sides of the hole cut in the ceiling. Make sure your garnish is deep enough to go thru and mask the sides of the ceiling hole. When we replaced an RV vent last year, the stock garnish was too shallow and we could see the foam component in the composite roof. The original garnish that was deep enough wasn't compatible with the new rv vent.
Good luck, it isn't a hard job. I would use an oscillating multi-function power tool to cut the hole instead of a jig saw or circular saw. With the oscillating power tool, you can be very deliberate in cutting the hold and go very slow to ensure you aren't cutting into any roof beam structures, wiring, or plumbing.