I can see the value of a vent line though and I am thinking running it to something on the frame for a filter as my fresh water tank is mounted under the flour of my teardrop and is like a gas tank mounted underneath the frame.
if bugs and dirt are going up your vent line into your water tank they do make a non expensive in line filter that goes in between your faucet and the fresh water tank like if you have a electric pump it would go between that and the sink faucet.
Mr. Cowboy,
A vent terminating just above your tank will help, but you will likely be much better off to have it a couple feet above the top of the tank.
A vent lower than that will allow water to slosh out.
A vent opening under the trailer would also invite road spray during a rainstorm, and anything else that is kicked up on a dusty road to make its way into your tank.
A filter is a good idea, but it is generally much preferred, and safer, to be sure only safe water gets into your tank to start with, via the fill port or vent, as once contaminants enter the tank, the tank itself is no longer "safe" for water storage, and bugs and junk can foul the pump and faucets/aerators.
Yes you can sanitize the tank, and no, a few bugs won't hurt you, but most folks would rather have clear clean water...
A filter on the incoming end of the air vent would be the easiest way to avoid problems.
I have a double layer of copper screen wire, and a piece of cotton cloth on mine, which is inside the trailer, to prevent bugs and dust from entering.
I guess I could get more serious and hook up some super filter, but bugs and dust are my only concerns.
Rob
Waiting for "someday" will leave you on your deathbed wondering why you didn't just rearrange your priorities and enjoy the time you had, instead of waiting for a "better" time to come along...