Silicon caulk tends to attract dirt and will look bad after awhile. There are several good caulking products out there, RV supply store should have good suggestions. I went with caulk putty tape, just remove or loosen screws inside the frame, pull outer frame away from the siding, and place the tape under the frame edge. I used a soft rubber mallet to gently tap the frame in until it squeezed most of the excess caulk tape out. I used clamps and small wooden shims under the clamp surfaces to slowly pull the frame in, tightening each clamp slowly and evenly. then used a sharpened popsicle stick, shaped like a butter knife, to gently cut around the frame to separate the putty tape, and removed excess. Do not attempt to pull the frame back in using screws inside. Frame is not that strong and will bend. Learned this the hard way on the first window I resealed. This is more time consuming, but I like the finished look better than caulking around outer edge of frame.
Retired Firefighter from Texas
2013 Jayco Flight 32TSBH