There may be a lot of sanding in your future. Silicone is tough to get rid of.
Butyl tape is just that, a tape - on a roll. So making a mess is harder to do. Not like caulk at all. Once you have it on, you trim off the excess. Might need some acetone to wipe off the residue.
As for sources, call around to RV parts places. Most will have it in grey & black and in various widths.
Not sure about cold damp conditions. if the butyl is flexable it should apply when cold. I would think you would want the surfaces dry.