I would recommend you use a vented system. They are not that much anymore, maybe something like a NuWay if your talking about large deposits of snow blocking vents that is entirely different than just a little coming through a window. If it is just the window maybe hanging a microfiber towel above a container with magnets or velcro in front of the opening would direct the moisture and keep other surfaces from getting wet. Possibly put the towel draped over the deflector a ways and close it in the door? Make sure air flow is maintained though. It is getting to the point with unvented propane that condensation and venting for me is just to much of a hassle especially with the many new cheap vented alternatives.