In my handbook it says to fill the reservoir to ward off condensation but nothing about stabilizer. It doesn't sound like a bad idea but I wonder if the oil would allow the stabilizer to thoroughly mix in the reservoir to do a proper job.
I would not add anything but oil to the VRO Tank.........If you are worried about condensation in the Spring (after WInterizing and sitting all winter) Just dump out the oil and add all new if it gives you peace of mind. Adding anything but Oilto the oil tank would Void your warranty should you have one. Seafoam is a Great Product, but use it as directed only.
Back in the late 60's or early 70's, when Marlin Perkins was Curator of the St. Louis Zoo, he started an extensive program for the breeding and hybirdizing of exotic speices........ He once tried for a scaled dog by mating the Taco Bell Chihuahua with Godzilla....... All he got was a hairy lizard.