Many RV windows use a rubber seal between the glass and metal. A U shaped piece that fits over the glass then pressed, fit into a channel in the metal frame. You can try to find a new seal or use a silicone sealer. If you use silicone tape the area with painters tape both sides of where you're going to apply the silicon. Spread a bead of silicone then with latex or similar gloves run a finger over the silicon to smooth it. Peel off the tape before the silicone starts to cure. It will leave a nice smooth seal that will be hardly visible. I've used this technique in various places, in the home and on the MH and it works well.