Apparently you have been very fortunate with your TC's & your right that I don't know about your campers etc. I just know that this is an apparent problem with these older Lance's. They actually sell a kit to repair this area (the wings). I have a dually truck (with mud guards) but it will throw a lot of spray up into the wing areas.
Once wood is wet its almost impossible to dry it out, (I know about this as I have restored a couple of Matthews Yachts) built out of mahogany & oak. Anyway my 93 880 had a 1" frame assy covered with 1/8" Luan over both sides. They covered this with a black tar paper like material on the inboard side & of course the outer metal on the finished side. This was a very crappy way to build a camper IMO, there was no way to really seal this.
This is where the steel staples & screws rusted away, you could literally flex these sides by hand. As mentioned earlier once wet you can't really dry it out & it gets dry rot started & hopefully one finds it before it moves into the flooring (plywood that will never dry out) or into the corner posts. Actually once the wood gets wet it starts a galvanic action & anywhere that a steel staple or screw is touching the aluminum outer skin it will eat tiny holes in the siding, because of the dissimilar metals, this is a real PITA.
And yes I am an expert on restoring old yachts & my old Lance. I replaced all the wood on both sides (lower areas) the cross pieces with clear fir & 1" marine plywood for the wings, all thourghly saturated with a marine 2 part epoxy. The epoxy when mixed with there powder to thicken it, it becomes stronger than the wood itself. So this procedure along with stainless hardware is really the only proper way to repair any old wood camper.
Basically my impression of my Lance was this: very beautiful & finished nice on the inside, top of the line appliances, upholstery, windows which made for a very beautiful camper. And still looks new after I had the paint matched & had all the jacks & bumper sandblasted then sprayed them to match. I just think that behind all the beautiful cosmetics that there really not built any better than the other top brands!
And yes I live in a wet area, & even though my camper has always been stored inside when not in use it takes a beating because of this climate.
I'm sorry if I offended you Travelnutz that wasn't my intent. Take care!