An 11 foot camper won't break your F250. The main thing to worry about is whether the rear tires are overloaded, that's your only real-world safety issue. They won't explode the minute you drive with 3 ounces too much on them, but the tires are your real weight limitation.
Go to a scale and weigh the thing, weigh the rear axle separately, divide by two, that's how much is on each rear tire. Find the fine print on the tire that tells the weight rating.
Remember that max weight rating is at max inflation, for heavy duty pickup tires thats usually 80 psi. If you're too heavy, physically larger wheels and tires can get you some "room" for your weight.
F250s have been hauling 11 foot campers since nineteen-O-nothing. It CAN do it.
However, I've said this a lot but here goes again, the first time you drive a dually with a large camper you'll never go back to a single rear wheel pickup again!
It won't have that creepy top-heavy scary feeling. That's the ultimate best way to go, and when you're talking about older models like you and I drive, they don't cost any more than single-wheel trucks.