Ughhh.... reading this thread was like getting kicked in the gut.....
So I'm a T100 guy too. I do have a Line-X spray in bed liner in my bed. All four turnbuckles are mounted \\ - as in pulling towards the front of the bed and cab of the truck. I have no metal plates on the underside of the bed for reinforcement. All 4 turnbuckles look like the following, the passenger rear side -
What I've noticed over the last year is that by not initially using a spacer between the camper and front wall of the bed, was that the FWC pushed that wall into the back of the cab. I have maybe 1/4 of an inch now between the top rail and the back of the cab.
When I took the camper off last winter I could see how bad I had tweaked that wall. About that time I saw Lawnmowerman's photo's. Following a few emails from him, I noticed the pinch welds he mentions. They were covered by the Line-X so I never noticed them. With that front wall pushed towards the cab, the Line X has started to separate just enough that I can see these pinch welds becoming an issue.
I also noticed after removing the camper that the front 2 eyebolts were bulging up slightly. Not much but bulging nonetheless. I had hoped to visit Ben last fall and have reinforcing plates added to the the bottom of my bed but time & finances didn't allow for that. Clearly this is something I need to address.
Regarding the spray on bedliner preventing the camper moving around, this is somewhat true. When loading the camper on and trying to align it correctly in the backyard, it is a SOB to move around. It takes me and a buddy to do it.
However, it can & will move on a bedliner with enough centrifugal force even fastened down with the turnbuckles. Let's just say you're driving out of Death Valley, south on Hwy 395 with the intent of taking CA14 over to Bakersfield. Let's say you miss your turn and don't notice until you're in Johannesburg.... Again speaking hypothetically, (

) let's say you get irked enough to do a "hasty" u-turn on Hwy 395. If not careful and without slowing down, the whole camper will shift, even with a spray on bedliner. Hypothetically speaking of course....
So I have little to add to this discussion other than yes, I'm starting to see some similar issues with my T100 & FWC combo. The spray on liner does help but it covered up those pinch welds from my sight so I wouldn't have put all of this together. And I usually hand tighten the turnbuckles and crank them one more with a screwdriver. They still will work themselves loose over rough and washboard roads. I could use Locktite or another solution but I just assumed that was part of the deal, having to re-tighten after time on rough roads.