The process of placing the skylights is similar to that of the windows, that is, to measure twice and cut one. Use a eletric saw and put silicone glue and seal.
We have two skylights, one in the kitchen area and another in the bathroom. In the bathroom the fact that we had a skylight made us not have to put a window and an extractor, because with the skylight the humidity of the baths has where to go out and the light has where to enter.
See here how we did the bathroom.
Lastly, there are several types of skylights, with various sizes. The best in our opinion are the ones that have a fan because they make an exhaust fan which should be very good when cooking in the van and when it is very hot, the problem is that they cost at least 200 €, the intermediates are those that have blinds and network musket, and finally there are the ones we bought that are the simplest and that the mosquito net does not move.