Do you really want silicone sealant? I tend to avoid if possible because not paintable. Five years ago I replaced doors and windows in my brick-built garage and used white Screwfix No Nonsense exterior frame sealant (acrylic and paintable) around them. After about four years it had shrunk slightly leaving voids in a very few places, which filled easily with a little of the same sealant (I don't think silicone sealant ever sticks to itself well). I never got round to painting it but didn't need to: after five years it is still acceptably white. I have found some SF No Nonsense products a bit poor but this one seems good.