The manufacturers do show a real concern for moisture build up in their owner's manuals. I blue tarped a motor home in the past without a problem. I think, in part it depends on how tightly it is sealed, but now I use a vented cover or leave my RVs uncovered.
Steve & Andra
2012 Ford F350 Super Duty 6.2 SRW Extended Cab
Current 08 Copper Canyon fifth wheel and NorthStar Laredo SC