I think you meant Mission and McAllen
Not sure what you mean by 'activities': organized events (think 'Missouri potluck dinner' or 'bingo night'), or amenities to use on your own...also not sure what's meant by 'caters to full-timers'
If willing to push into Brownsville, there's a new place called Tropical Trails RV resort (https://www.tropicaltrailsrvresort.com/)...no age restriction...I'm sure the long-range goal is to become a 'Winter Texan' park, but for now they take what they can get (brand new, so very little word of mouth....and, as a bonus, COVID struck in their first months of operation)...we're me, dw, and our 14-year-old
Space distancing is adequate for privacy, and (in our most recent weekender there (October 2020)) the resort still pretty much empty...acres and acres of unused RV spaces....spots seem big enough to handle pretty much any rig
The place has a nice clubhouse....showerhouses and laundry (two, I think)...exercise/rec room...pool...
We're not 'joiners' anyway (prefer to do our own thing) so it works great for us when we need a 'rest and relaxation' weekend without the hassle of long travel or lead-time planning (because it's so empty, no chance of getting turned away/no need to do an advance online booking)...but, for folks who look to a park for social activities, Tropical Trails probably has little or none of that because so few people...best you could hope for would be chatting with 'new friends' at the pool or something.
We usually state-park camp, but have hit Tropical Trails when we wake up on a Saturday morning, look at each other, and say, 'let's roll'