The mastic tape is good stuff, but its difficult to get it in narrow widths, as its used more for bedding down hatches, or aluminium awning rails and the like....
Like pensioners says, I'd be inclined to use a silicone to bed it on, it will stop the dirt and water getting in and you can make a nice looking job using not much more than some kitchen paper and a damp finger, to clean away any excess and leave a good finish..... Oops.....Health and Safety
has just whispered in my ear that damp figers are no konger approved devices for use on sealers of this nature and a spatula is now generally recommended :cheer:
I have tried to cut mastic into narrow strips ( about 4mm wide), but its not easy and the silicone seems to last quite well and is easy to apply.
Regards
paws