Well, I replaced the skylight earlier this week and it was actually a fairly straightforward job. I did uncover shoddy work by a previous person, but I don't blame it on the older couple I bought it from as the gentleman didn't like heights so no work was done directly by him. My inspector did identify it as a problem, but we just thought the tape and sealer was old needing replaced.
I decided to replace the skylight with a smoked version to cut down on light entering the coach since the existing lens was old. I scrapped off the tape and existing sealer to uncover the screws, and things seemed old compared to the videos I watched online. The old skylight was tough to pull off due to excessive butyl sealant. Once it was out of the way, I realized why the skylight looked odd on the roof. The sealer and tape looked separated, but that wasn't the main issue. The skylight had been replaced previously, but whoever did the work didn't remove the prior skylight. It appears they cut the dome off the original skylight, and then just dumped a bucket of sealant on the old lip and screwed the then new skylight on top. That's why there was a huge gap. It's unbelievable that someone would do that rather than do the job correctly.
I removed the gallon of sealant and old flange, and the frame underneath was quite nice. I cleaned it well, and then installed the new smoked skylight correctly. Once done, I used Dycor lap sealant but it's didn't flow as well as expected. It moved a little, .5 inch or so, but it really didn't level out like the video's showed. It's sealed fine but I just don't like the lumpiness of it.
I also replaced the vent on the roof since the cap was cracked at the top. It was an easy repair by comparison.
I cleaned off the roof where it was dirty, but I'll need to plan another trip up there to give it a good soap washing so it's more presentable. No one will see it, but I'll feel better knowing it's clean and nice.