Hello there! In my Questions From the Road column, I take a crack at answering real questions from real RVers, just like you. You might find your question here! If not, please send me an email!
I’m sure you’ve already guessed that cost is a factor. Another issue is that there’s this idea that “the aftermarket will solve [X] problem.” And even though not all manufacturers feel that way, cost competitiveness forces everyone to the lowest common denominator.
Another reason is OEM stipulations. Guess who controls the dimensions, clearances, and design of the refrigerator vent? The refrigerator manufacturer. Guess who controls the vent conditions of the furnace vent? The furnace manufacturer. And so forth. RV manufacturers have to abide by these rules.
If the RV manufacturer places an unapproved cover over the vent, the RV manufacturer automatically assumes all liability for any and all failures! And not just failures of the vent, but of whatever the vent protects! And no manufacturer wants to be on the hook for a $1,000 fridge.
Some RVers install aftermarket covers to prevent rain-driven leaks, others to stop mud daubers, mice, chipmunks, beetles, bees, and other critters from getting into your RV. A popular aftermarket add-on is “mud dauber screens,” which cover up the intake and exhaust vents of most propane-burning appliances. These do work to keep out wasps, but if they get clogged, they can mess up an appliance in all kinds of ways.