Some tricks.
First, if you plan on removing it again, use vinyl tape on the hull where the silicone will seal to the hull. You can but electrical tape in numerous colors, that's what I use. Just tape off where the sealant will be on the hull.
You can trim the excess with a razor blade. Then just seal it up normally.
Next, rub an ice cube on your finger before smoothing the excess sealant, it won't stick to your finger and come out incredibly smooth.