That's a brand new TT - as in a 2018?? Yikes. That is unbelievably bad for a new TT. Looks almost like it's been sitting in salt water for years. That is NOT normal.
If that's rust that you can see, there's going to be more of it behind the coroplast underbelly too.
If the dealer and/or manufacturer refuse to do anything, I'd take it to a reputable frame and axle shop and get it inspected and get a report that you can send to the manufacturer. We did that on a previous TT that had frame problems (not rust related) and we eventually got it replaced with a whole new TT.