I know I am late to this discussion, but I have used both Pop-up and Travel Trailer (RV).
When we were kids (4 of us plus mom and dad) we went camping all the time. We had a Popup with Canvas Bunk Ends. The kids slept in the pop-up while mom and dad slept (on cots) in a Canvas (not Nylon) tent. We would also set up a "Shelter" which was about 15x15 foot screened in area. This was our "Kitchen" area. Unlike most pop-ups now-a-days, ours was strictly no-frills. No electric, water, sewer, fridge, stove, etc. We had the bunk ends (that could comfortably sleep 2 people on each end) and the center table area that would convert to another bed area (that could easily sleep 3 people and probably 4 if needed). When set up as a table you could "Squeeze" 6 people (3 on each side) at the table.
In the heat, however, the camper would get HOT. You could "Unzip" the windows and hope for a breeze but it was still hot. We had 5 gallon water jugs that we used for our water needs and filled them up daily. As "Kids" we had a little "Potty" chair to use for night time so we didn't have to walk to the CS in the middle of the night. (also this was not at Disney). So while it may sound like this is terrible, it wasn't. We loved it and it definitely would give you more of the "Camping" feel (as ed pointed out).
Now that I am older with a family of my own (me, DW, DD17 DD10 and DD17's BF), we go camping (and to the Fort). While I would be happy with our old pop-up from when I was a kid, My wife needs more "Creature Comforts" (hopefully not to many creatures though). We have a 27' Travel Trailer. It is nice to have A/C and a kitchen as well as TV, Refrigerator, and of course a toilet and shower (albeit small). We were like having the facilities in the camper, but tend to use the CS in the fort, and tend to eat our meals at the parks or out (last time we got the
DDP so why not use it right?). It's also nice to have the space to move around it if the weather is not so nice. It is however still cramped in the Travel Trailer so I expect it would be more so in the Pop-up. For us the Camper is mostly about a place to lay our heads down at night and to take a break from a day. (at least when we are at WDW). The Trailer does allow us to "Camp" but it's not quite the full camping experience. (Give me a tent and a sleeping back to really get the experience)
As Sundancer330 points out, I could imagine that a Pop-up (without an A/C) would get EXTREMELY hot in the summer time. If, however, you are planning on spending the "Nice" days Out at the parks/pools, then I think it's less of an issue. The Bad weather time (such as Rain) wouldn't be as hot anyway. Although I don't know for sure, but I know many pop-ups now also come with an A/C so that would make it bearable.
Really, I think it depends on how much of the Camping experience you really want. If you are ready to go full into camping, go with the pop-up. If not, go with the Travel Trailer (RV). Just know that there are advantages and disadvantages to both.