Hard to tell, but almost looks like the cosmetic tape over the panel joints......, and I agree a dealer service warranty inspection is best.
I would insist that your RV dealer generated a service warranty document so you have a paper trail (get copy)......, irregardless of the dealer's inspection determination.
2016 GM 2500HD 6.0L/4.10
2018 Jay Flight 24RBS
2002 GM 2500HD 6.0L/4:10 (retired)
2005 Jayco Eagle 278FBS (retired)
1999 Jayco Eagle 246FB (retired)
Reese HP Dual Cam (Strait-Line)