If it is an exterior leak, you remove the leaking item, clean the sealing surfaces. Apply butyl putty tape to one side, and screw the item back to the trailer. Then for extra credit you might drape a bead of Geocel ProFlex caulk over the top of the flange seal, and down the sides a bit.
I'd wait on the caulk until the putty tape has squeezed out for a good while. Otherwise when it does squeeze out, it will dislodge the caulk. Anyway, there is lot of info on RV sealing and caulking here, on Youtube, etc.
And I'll agree with NO, don't use silicone. Use the ProFlex or something similar.