Howdy neighbor!
I'm not far away from you over in Hoover, AL and if you already own the pop-up then the business case to prove in staying at FW is an easy one. If you're going to stay in a Disney hotel, you're paying for the gas mostly anyway. The only delta is the lower MPG you get pulling the camper. For us with our pop-up it is about an extra 10 gallons one-way which is, what, about $35? Given that you can stay, depending on season, for about $35 less at FW than you can at a Value resort (a partial site for $47 versus $82 for a Pop-Century room), you make that up in one day at the Fort; in two days you covered your round-trip delta already.
In fairness, I don't think FW compares to a Value; it's at least a Moderate IMO even staying in a campsite and not a cabin given the availability of shopping, entertainment, kid programs, and landscaping, and atmosphere. Plus we're not trapped indoors in a room - we're outside in nature and wide open spaces so it's more relaxing. We go for 4-6 days usually but only go to the parks maybe 2 days. We leave 2-3 days to hang out at the Fort, swim, do the organized kid programs there, boat, bike, maybe skip over to Downtown Disney. True, the FW pool is not as themed as other resorts but it is nice and due (supposedly) for an overhaul soon. Plus we love the campfire and sing-along every night (free!).
One real benefit of staying at the Fort for us in our pop-up is we eat in more often (we have our fridge, our stove, microwave, pots/pans etc) so we eat healthier and cheaper overall. We do one or two sit-downs as a splurge per trip but with 3 kids 10-15 years old wanting to order off the adult menus, you can run up some big bucks real fast at Disney (the $125 lunch for 5 at Rainforest Cafe comes to mind REAL FAST

). We pack picnic lunches into the parks (store it in a locker) which helps. If you have a hotel room with no stove, no grill, no fridge, you're trapped into food court food for every meal with counter service or more expensive table service.
So we choose the FW/pop-up route to keep costs in line so we can go to FW more often. Plus, as BigDaddyRog said, I can't imagine being trapped in a hotel room. I like my wide open spaces, my quiet morning walk to the Comfort Station, watching the bunnies and wild turkeys move around the grass. I guess it's a lifestyle choice that also ends up being economical for us.
Roll Tide!
Bama ED