I use megs tire gel on my tyres (duh).
I apply it using the curved side of a kitchen sponge...
I then use the residue to do my trim.
Not only is it better than any other trim product in terms of lasting and blackness but it save me buying two products (without using twice as much of one product).
The shape of the sponge also make applying it so easy!
Just dont be tempted to put extra on (ie not just using residue) as this will run and go on your paint (the residue alone wont). Its not harmful but it doesnt look good.....