Just wanted to pass along a situation I encountered over the weekend. My Oasis 18BH is my first travel trailer. I bought the screens to cover the water heater and furnace vents after our last camping trip a couple of weeks ago, and installed them. I decided to wash my TT the next weekend. Upon finishing up and going inside, there was a puddle of water in the floor just in front of the bathroom door, and between the furnace outlet and the galley cabinets. I looked around the ceiling and AC unit, and found no evidence of a leak in those areas, but did notice a trickle of water coming from under the lower bunk to the left of the furnace cover. When I removed the cover, I saw water coming from under the furnace. I cleaned up the water in the floor, and ran the furnace for a few minutes to make sure all was OK, and then just wrote it off to maybe inadvertently spraying water into the outside vent on accident.
A few days later, we had a pretty good rainstorm. I had to go into the TT to get something, and again there was a puddle of water in the same place. Until I installed the screen over the furnace vent, I had no issues with water during rain. My assumption is that where the screen sits over the vent screen, I should have sealed with silicone or putty tape or something. The way the vent is, the screen actually created a drip edge directly into the furnace vent, so I believe it actually channeled the water into the vent thereby causing water to run out of the bottom of the furnace and into my TT. I have since run a bead of silicone around the vent screen, and also added a sheet metal "roof" over the top to divert water off the edges, and ran a bead of silicone across the edge that meets the camper/vent. Don't know if anyone else has ever come across this issue or not, but maybe it will help someone in the future. We've had no rain to fully test it out, but I think this should fix my issue. The installation instructions for the screens made no mention of needing to seal around them, so I'm not sure if this is an issue with the style of vent on the Oasis or what. There was some info online about needing to seal them using putty tape or silicone, and installing the "roof" to further guard against water intrusion. Anyway, just my experience.