Make your life easier and invest in a Silicon profiling tool like Fugi or similar and watch a couple youtube videos beforehand, if this is your first go at sealing all this type of stuff it can be a very messy job
A set of fugi tools are a must and plenty of blue roll and wipes I use Silicon spray for smoothing off after , don't apply to much Silicon in one go you can always add some more it's a pita to remove excess . Kop