after i rolled an flared my rears, i ground back the inside as best i could, an put a big smear of rtv silicon all the way down to the bottom of the fold, then neatly blended it in. This way no water should get in or out under ur lip
just need to go nice an slow when doing it too, stretch the metal slowly not too quick. aim for about an hours of hitting each side, its not a 5 minute job
in theory by skinny white boy