First of all he is wrong. Search the Internet and you will find entries noting wide variation in front axle loading from none at all to a good bit. Think about where the center of gravity of the camper is in comparison to the axles and then the wide variations in options and how the camper is loaded.
I have done exactly what you ask. Here my weights from my CAT scale tickets.
F350 with driver and shotgun Fully loaded ready to head West with camper
Front axle 4,440 Front axle 4,740
Rear axle 3,200 Rear axle 6,080
Total 7,640 Total 10,820
As you can see, ready to roll, I am just squeaking in under my 11,000 GVWR and actually am over the 6,000 rear axle weight (carrying less water I can hit it). This is with a pop-up camper that has a base weight of 1,643 pounds dry weight according to the manufacturer’s website.
The loaded weights include an ice chest behind the front seat, a few tools, and odds and end, so the TC by itself did not even account for the entire 300 pound change. Plus I have
30 gallons of water right at my front wall and i have moved my two AGM batteries from behind the rear axle to against the front wall of my camper. If it were not for those changes plus what was in my cab, I bet my front axle weight would not have changed or changed very little.
I am sure others have done the same thing and found theirs is much different than mine. I am curious where your mechanic got his numbers. Are they weighing truck campers now at Dodge dealerships? The reason I ask is I am finding, despite all the posts in the truck camper forums on weight, darn few folks seem able to produce real world numbers from CAT scales.
My two cents
Steve and Andra
2012 F350 6.2 gasser SRW LB
Fab Fours front and rear in case we run into a rhino
2019 Northstar Laredo SC