The metal is "butted" rather than overlapped, a very vulnerable construction method, not to mention leaky.
The edge trim is not J rail but L rail, wrapped around and sealed on both sides.
If there is any way to buy new roof metal and overlap the walls, I would do it. The old Shastas (54-57) were butted at the lower corners and the two here haven't leaked in that area. Dinette windows, yes, edges, no. Granted, there was wonderful old cloth backed putty as a seal.
My thought is, if you could at least overlap the roof area, you would be ahead of the game.
I changed the front and rear metal on the 57 Shasta for that reason. For some reason they overlapped the top but not the front and rear metal. I got new J Rail and overlapped the new metal so that the entire trailer was overlapped and j railed.
God grant me the strength to restore the trailers I can, The courage to strip the parts off the ones I can't, And the wisdom to know the difference...
I discovered that the aluminum was cut very uneven on the current Shasta I am redoing lap varying from almost none to an inch or more so I trimmed the long areas and installed an angle formed rail that wraps around both sides in order to insure a better seal. Time will tell if it was a good idea or not. Since this is my own trailer and I have no plans of selling it I have tried several things that are outside of normal practice but that I believe will make it better/ more durable. Only time will tell.