The soft "Lifeventure" towels available from outdoor shops are great for covering the camera in rain and spray and are also soft enough to wipe the filter. They are much thicker and more absorbent than lens cloths yet very soft. I use one with my Lee resin filters quite happily, so should be fine for your Hoya glass one. Best to remove spray before it dries, otherwise concur soaking with deionised water before wiping.
In misty/spray conditions, I insert another filter in the front slot which gets removed (covered in any spray) just before making the exposure.