Assuming the vaccines are successful, we are probably looking at 2022 before we see a big dumping of RVs (if that happens at all). A lot of people will still be nervous about air travel for a year or two. Others having dumped so much money into a camper will keep at it for at least a few years.
So probably by 2022, you may see deals on used RVs but I wouldn't count on reduced numbers at campgrounds for at least a few years.
Plus keep in mind, it's not unusual for a family of 4 to dump $10k into a 2 week vacation...so I don't think people are going to panic over a $20k RV sitting in the back yard.