Since we don't know about your lite fixtures, will tell you my overhead lights mounted in the ceiling can be pulled down out of the hole they are mounted in. They are just held in place by springs. I have often pulled one down to see what is between the ceiling and roof. My bathroom has one of the fixtures in the ceiling. It allows a limited view of what is up there.
In a different post one of the forum members suggested getting an endoscope from Amazon which allows you to use your phone to see in tight spaces. Not just in the RV but your home, car, etc. They are not terribly expensive. Here is a link: https://www.amazon.com/s?k=endoscope...s_ts-doa-p_1_4
Mine is to be delivered within the next week. Can hardly wait as I have several spots I want to look at in my RV and in my home.