Trailer full of flies ??

I tend to get a lot of flies in my shop and I've found the best deterrent is those old fashioned sticky hang up glue strips.

Maggots do have a useful purpose... Fish bait. Flies have no useful purpose except irritation.

darsben1 wrote:
0ne fly today lays eggs and generates up to one hundred flies a day. A fly can live up to 30 days

Yep.

If you have one or two flies, it came in through a torn screen, etc.

If you have a "bunch of flies", then there is something in the RV that is feeding the maggots.

I'd be checking to see if there is a dead rodent body or, more likely, there was food left somewhere to rot (much more likely if there are kids around).

Gee, a baby fly is a maggot. You have maggots then flies... Isn't that comforting?

0ne fly today lays eggs and generates up to one hundred flies a day. A fly can live up to 30 days

Neither of those appliances are 'connected' to inside of rig unless fridge was poorly installed and not sealed or furnace heat exchanger had a big hole in it in which case CO from combustion would be getting inside RV.

House Flies inside........
Come in thru entry door, open window without a screen etc

Gnats, sewer flies...
Come in thru waste tank drain valve that is left open. Grey or black....set up house, invite cousins/friends to join them then fly out when you flush toilet or up thru drain line when a 'P' trap goes dry.