There are a lot of cabover rebuild threads over the course of a year in the TC forum. In their case, I think many of the leaks occur in the bottom edge molding. That is a problem design, found on many types of RVs. The side lip (or flange) on the molding points up, and catches water. I had to repair some damage at the rear corners of an old aluminum side fiver. The side view of the corners looked like "<". There was no damage on the upper half, but there was water entry on the lower half. Even though the lip on the lower half of the molding didn't point straight up, it was upward enough to catch water and channel it inside.
Since then, I've been using Proflex RV caulk on the lip edge of moldings which face upward. Same for top edges of windows and other attachments. A few years ago I noticed a trailer in a Jayco showroom, they were doing the same thing. They wrapped caulk over the windows, stopping a little way down each side. So the upward facing flange is the problem, not the verticals or downward facing flanges.
My current Forest River Sunseeker has a micro bead of caulk around almost all of the problem areas. However, the tiny bead requires frequent examination, as it doesn't have much long term staying power. My second fiver had the same type of factory caulk application, and it was pretty iffy after several years. More on that below.
The cabover problem is not reported much in fivers. It's just a completely different design, with the frame fully supporting the whole body from end to end. And the sidewalls are one piece all the way. The upward facing bottom molding is still there though, and I think they do catch water. My second fiver didn't show any water damage, but several of the molding's screws were rusted out inside the molding.
The problem of roof molding damming up the water on the roof at the front and rear transitions is common to any RV other than a molded body, bus, Airstream, etc. This was a source of water entry on my first fiver. After I repaired the damage, I used Eternabond tape on the dam corners. Pun intended, I guess. :)
Every, and I mean EVERY, thing attached with screws is a potential point of entry. On the old fiver, on which I removed some of the siding for repairs, there was at least some water entry on taillight screws, on the screws for the little plastic hold-open latches for cargo doors, and on and on. Start viewing every horizontal molding, flange, or object, and every screw for same, as evil water catchers, and you'll get the idea.
On a Class C filon cabover, I would think the order of likely culprits would be, in order:
The bottom flanges
The roof transition from roof to filon cap
Front window rounding out the top three.
And everything else way down the list
