My Dutchmen dealer told us the same thing.
My TT has the vinyl coated wallboard with a clear "tape" over the seam where the wallboard meets the shower floor. Used it "as is" all summer with no issues.
I am diligent about using a squeegee on the wallboard after a shower, although I don't know if I need to bother.
I was most worried that the weight of the user moving about in the shower would pull that seam tape away from the wallboard as we are pretty big people - think elephant in a phone booth. That has not been an issue, either.
2016 Shasta Oasis 18BH, 2015 Ram1/2 ton Hemi