Appropriate amount of rocking

Yes, Alex has it right. How much frame flexing, both fore-to-aft and side-to-side frame flexing should you expect? It really depends on the frame of your truck and the year. Older Fords were made to have a lot of flex, especially the long wheel base models. The newer the truck the less frame flex you get, IMEX. My short wheel base Ram with a hydro formed frame and enough cross members has little flex; by design. I was starting to get some fore to aft 'rocking' and found that one of the four 3/8" bolts holding the bed onto the frame had pulled through the anchor tab and was floating. 3, 3/8" bolts holding the entire 2500 pound bed and TC to the frame of the truck. Scary. The other issues are your suspension and your shocks. I use the Lance struts. I still like the 14 yr. old ones I use on every trip. It just tightens things up, like too-small underwear. 8<) For porpoising, it's the best solution, ..so far. The pros and cons of Lance struts have been beat to death on here, mostly the nays are by people who have never had them, and the yeahs are principally by people who have actually used them. Just know this: they make some difference, but are not the do all; fix all for stability.
The other issues are your suspension and your shocks. I have done a lot of fine tuning to reduce the sway, pitch and yaw, and off-road is a whole different animal to deal with. Recently, I replaced the front and rear anti sway bar rubber, 4-link bushings and most of the Gen II steering components with newer Gen IV versions. This 15 year old truck is very tight now, almost like new. Why not like new? I would say the body bushings holding the cab and bed to the frame are getting tired. Am I going to address that? Nope, the next owner can deal with that issue.
To really address rocking and sway reduction the thing to do is get WAY more truck than you think you will need. A 4 or 5 series truck will keep you far from the wobbly situation you get with a low rated 2 series truck. Of course, there is no free ride. The ride in an MT 4 or 5 series will rattle your teeth, unless you get the new air ride. 8<)
jefe

Ford truck do have a lot of frame flex, due to that I go off road with my rig I have about 5 inches between the cab and camper overhead to keep cab slapping from occurring.

You can tighten the turnbuckles or even bolt the camper to the bed. You will still see the rocking; i.e., the distance between the roof of the truck and camper will move. The truck will flex between the cab and bed. For most rigs, you need to allow at least 1-2" of clearance.

I also see it, and understand its normal, but always wonders how those struts you see on the Lance campers, that go from camper overhang to truck hood work. I assume they are like gas struts? you can't have something ridge there as something has to give.

I have a 95 F350 with a heavy camper and mine does the same I have movement also between the cab and camper due to the frame flex

Just make sure your turnbuckles are tightened appropriately for the type you have. Your description sounds pretty normal.

If your camper is sitting level in the truck bed and your tie-downs are tight, then ignore the cabover movement....it means nothing....it is actually the cab of your truck moving slightly differently from your box due to frame flex.....if you look in your mirror at the camper in relation to the side of the box you will see that the camper is not moving in the box.....I have been carrying campers for over 25 years and pay no attention to the independant movement of camper and cab.....slowly drive diagonally over a speed bump and you will see how the truck frame torques and moves box and cab differently.....