One of the comments I've heard most, from RV workers, dealers, RV tech's and DYI owners, is don't use silicone caulk, it is terrible to remove later.
As far as what and how to use, first remove old caulk with a plastic scraper. If some caulk does not want to "break" off, use a sharp utility knife or better yet an exacto knife (it gives more altitude and movement), carefully cut a "V" down into the seam you are sealing, so it comes off. Do not cut to hard or to deep, you don't want to score/cut the fiberglass. Then clean with mineral spirits, till all residue is gone. On all seams on the exterior fiberglass gel coat, use SilapreneŽ blue
. That is what they use at Cedar Creek and most other RV manufactures. After you have caulked an area, use a spray bottle with a 50/50 mixture of mineral spirits and water, shaking it now and then to keep it mixed. Spray where caulked, then use a rubber/plastic scraper to create a "smooth" caulk line. If you want a little "bubble", use a rat tail file and cut the size of "bubble" you want on one corner, then use that corner to remove excess caulk. For anything on the roof or at the edges, use Dicor self-leveling caulk. Once you get the hang of it, it is easy work.
Hope this helps and God bless,