At our seasonal camp site and when NOT using our TT, we open TT's roof vents approx 3". We lock all doors and windows as well. Except for our small kitchen window. Its "locked open" approx 3". Thus, creating natural air flow venting in this little indown crack, inside our TT and out the top roof vents. When we return to our seasonal TT each weekend, its insides smells nice and fresh - from this natural venting.
With Maxxair or VentMate roof vents (white on our bathroom and black above our kids bedroom area), we can now leave our TT's roof vents open - without rain getting inside as well. For this reason, roof vent covers (Maxxair or VentMate company) are worth it.
To me, Roof vents should be minimum build....