Water may well trave a bit before it becomes visible especially when travellingl
Or where the roof meets the sidewalls.
Having has a water problem I use a combination of Captain Tolley and
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I "painted this" on the roof by and on the seams about 3inches wide.
And on the join between the hab roof and the cab roof
Our roof is similarly flat !
The product is clear and you can see it has been done (just) but it is out of sight.
Nothing worse than a leak
BTW we appear to have survived the latest downpours