I have an older Ranger (2000, super cab, 4.0L V6) with a newer camper (2010, All Terrain Camper - Bobcat, the equivalent of the FWC Eagle). I know that we have at least one or two other WTW forum members with something similar, so they should be able to add to the discussion.
Height:
It will depend greatly on what size tires you have, what type and stiffness of rear leaf springs you have and the height of the camper from bottom to top (which is a little different between FWC Eagle - taller and my ATC Bobcat - shorter by an inch or two).
You should be able to get the seller to get you the measurement for the height of the camper you are purchasing, then add that to you truck bed height, subtract 1" or 2" for rear leaf spring sag and you'll have a good estimate.
Mounting:
On my Ranger I have the following "in the truck bed" tie down eye brackets.
Eye brackets
I wanted to easily remove the eye brackets when the camper is off the truck and I can use my removal-able plastic bed liner.
I've never had an issue with these, I think they are very strong.
Forward bracket, as far forward as possible, same on the other side.
Rear bracket. I'm not sure if your FWC will be the same as my ATC.
Note that the rear gas tank filler clearance stamped into the bed (that Ford never made a gas tank for, but some guys use a Bronco II rear gas tank) may need to be hammered down so the camper will sit flat in that area. When I ordered mine from ATC, I was given the choice of doing the hammering, or have the camper section modified (by cutting the wood corner in a triangle fashion) where that unused filler was stamped into the bed. You can see what I opted for, I wanted the interior of the camper to not have that triangle cut out.. Take a 2-3 pound, short handle sledge hammer with you so, if it needs to be hammered you can do it. I did eventually clean and paint the area.
If you only mount the eye brackets through the place where the truck bed has a double layer of metal, then you would be OK. That is the way most of the camper eye brackets are mounted. However, I wanted a direct link to the frame rails, so, I made some brackets that mount the truck bed eye brackets to the frame rails. I am often on very bad dirt roads, so far, no problems with the brackets I made below.
Bed to frame brackets.
Turn Buckles.
The previous owner should have the turn buckles for you.
On your way home, stop every now and then to check that they are staying tight, but NOT too tight to pull out the eye bolts in the camper.
Some guys have experimented with how to keep them tight and not coming loose, double nuts, cotter pins, you'll find several threads in the WTW forum on these details.
Bed cushioning and anti-sliding.
I got this floor runner at my local hardware store. Protects the bed of the camper, in your case the spray in liner, and it's slightly sticky, so the camper doesn't slide around.
There are other similar types of options available, I think you'll want something.
Carrying the weight.
Suspension.
I think you'll find that getting the camper home the first time will be an interesting experience. Take it easy, go a bit slower than you might normally drive, allow a lot more room ahead so you can stop when needed without an incident and when you get home, think about helping the truck carry the weight.
I tried air bags and that did an OK job, however, it was more for left/right leveling of the camper as one side of the camper is often heavier than the other side (cabinets vs no cabinets). I could pump both airbags independently and to different pressures if needed.
I eventually did what other Ranger owners have done, get stronger rear leaf springs. I went with a 4 leaf pack, which was double the stock two leaf unit. When I don't have the camper on the truck it is a real rough ride, so, I lower my tire pressure. However, when the camper is on the truck it is just right for me. Note, I built my own interior and I think my camper comes in at a lower weight than a factory built interior.
I don't have the FX series, it wasn't around back in 2000 when I purchased my truck new. If your FX has a 4 leaf rear pack already, you may be OK. I think Ski has gone to a 7 leaf pack from Deaver Springs, however, I believe he keeps his camper on the truck all the time.
Tires.
Your original tires will probably need to be upgraded to a "D" or "E" (better). I have the 15" wheels on my Ranger, so, the highest rating for that wheel size in my choice of tires was a "D" rating. They work great for me. You can air down when you think you need to soften the ride or get more traction by widening the footprint, and pump them back up when you get back on pavement. Lots of threads on tires here in the WTW forum, look them up.
Well that's about all I've got at this time.
Time to get to work.
Good luck and congratulations.
Happy camping to you, until we meet on the trail...
