If you want to "join" other people camping or have them join you, you may want to try announcing "I plan to be at XYZ RV Park (or Campground) on (Dates)" in the "Rallies & Events" forum. If it is a popular place that you have to make reservations months (or years) in advance, take that into account when announcing your plans. An informal gathering will probably work better than a formal organized "rally".
Once upon a time, the informal gatherings were how it was done. There were very few big rallies. Early "Bulletin Boards" always had a spot for people to say where they would be for informal gatherings. Sometimes people would do a "campfire" gathering and toast marshmallows. A more involved gathering would have a "bring your own" uncooked food item (along with plates, eating utensils, napkins, soft beverage, etc) and the food would be tossed on a gathering of grills to be cooked. Some did that for breakfast where you put a couple beaten eggs into a labeled zip lock freezer baggie (each person had their own baggie) and it was tossed in a pot of boiling water to make a "sous vide" type scrambled egg. Of course this was back when people "camped" as opposed to "RVing". It allowed people to provide their own food that suited their tastes, dietary needs and pocketbook. Things were a bit less organized and structured.
A gathering might be as small as two campers or as large as 20 campers (that would be roughly 30+ people which is a large group if you think about it). The smaller groups could easily fit into most campgrounds without disrupting other campers. It was not only more informal but more intimate. Places and ideas were shared more readily. This is how people developed the long lasting friendships you hear touted about when people talk about how great RVing is/was. Usually the only rules were no drunks, no drugs, no fights, no politics and no religion. Since these gatherings normally happened in public campgrounds where (at the time) no drinking or drugs were allowed, the drink/drugs were usually not a problem. An emphasis on "family friendly" was placed on the gatherings since many people camped with kids in tow.