Welcome to the forum.
Roof seams/seals are something that the dealer should have found during a PDI (Pre Delivery Inspection). Not all dealers do everything they should to insure the unit is really "ready to camp". Since your taking it back, I would take pictures. Then ask the service writer to have a look.
If he/she says it's "good to go", you might escalate the concern to the service mgr. The dealership should do the right thing and fix any "voids", the key is voids need to be sealed, crooked/sloppy lines may be ugly but if the seam is sealed you may not have a case.
2012 Copper Canyon 273FWRET being towed by a 1994 Ford F350 CC,LB,Dually diesel.
Airlift 5000 bags, Prodigy brake control, 5 gauges on the pillar.Used to tow a '97 Jayco 323RKS.
Now an RVIA registered tech. Retired from Law enforcement in 2008 after 25+ yrs.