I have a 1998 Lance 845 on a 2005 GMC 2500HD. The 845 is an older version of the 865. It has a claimed dry weight of about 1800 lbs. The GMC has a payload rating of 27xx lbs (I don't remember the exact number). I am about 350 lbs overweight. That means my 1800 LB camper, after loading in batteries, water, propane, food, etc plus all my stuff, weighs about 3000 lbs. That is the real weight. Dry weight is not real weight.
This is what these people are trying to tell you. Don't believe the "F150 filter" on the Lance website. If I set the filter to 3/4T (what I have) it will tell me I can carry a camper with a 3000 lb dry weight. That will be about 3800-4000 lbs real weight, on a truck with a 2700 lb payload. I would be 1000 - 1300 lbs overweight, and well over the axle and tire weight ratings.
I think all camper mfgs will tell you a similar story. They want to sell you a camper. They don't much care if you are happy with the result, or even safe.