Hi CF,
The biggest thing is you will need to put the camper on a frame of wood between the bed and camper because of the difference in the bed sides vertical height. Contact Stan at Four Wheel. stan@fourwh.com. He can tell you the thickness of the platform you need and may have some pictures, plus give you any other info you may need to know.
What truck are you putting it on? If it is a Toyota it fits the Tacoma 1997 - present and the first Gen Tundra. Tundra is the same width as the second Gen Tacoma and 1 foot longer because it came with a V8.
When we ordered our 2012 Eagle we had it built to fit on a second Gen Tacoma. because at the time we couldn't afford a new truck. The following pcs show it on the '99 and 2013. On the 2013 there is less than 1" space between the top of the rails . On the '99 about 4 inches. Pictures don't show the difference. More obvious if you look at the distance between the top of the cabs and bottom of the camper.
Hope some of this info helps. Good luck on your decision.
Forgot to add Suspension comment
You will need either air bags for part time camper carrying or New rear springs for full time. On both trucks we added a new " rear spring set" to support 1,800 pounds and "E" Rated tires. '99 needed a 6 leaf. 2013 a 5 leaf. The camper is bolted down full time.
The second and third Gen Tacoma's have a plastic bed. I had my welding shop weld plates on the frame to bolt to. In over 8 years and 67,000 miles the bolts never came loose.
If you want more general info on the Eagle check out my post. The link is under my signature.
1999
2013