Regarding Bigfoot, and other trailers, the roof is not the only place to experience leaks. If window caulking is left unchecked, especially on Bigfoots, water WILL seep into the insulation and walls. Couple of tricks to help deter this. 1) it is very easy to remove and reseal the windows. You may even find room for added insulation. 2) You can buy flexible rain gutters that you cut to length and mold around your windows to alleviate this issue.
Now, Bigfoots have a radial roof. Water will flow down and streak the sides, including the windows. The rain gutter will be one of the cheapest yet most important modifications you can do. Bigfoots are wonderful trailers, especially if you like late fall and early winter camping! Not roomy, but efficient, especially for dry camping!
Hope that helps.