There's a product called "Webzone" which is an inceciticide for crops. It's as dear as poison, but a 1 litre bottle will last for years if only using it around the hose or camp.
It's safe for "food preparation areas" and dosn't smell too bad, but it's great for killing all sorts of bugs and keeping flies and mozzies and sandflies away.
I have a 9 litre spray bottle of it made up and I do around the house and farm to keep the redbacks down and fleas and ticks around the dog area.
Spray it under outdoor tables and chairs and that will keep flies away for a few hours at least. Spray it inside the bottom of the tinnie when out fishing and it'll keep mozzies and sandflies away.
It's a residual type spray, so if you spray it around the wheels and legs of the camper and around the edge of the room area , it'll keep creepy crawlies out of the tent and trailer.
No good for bees so dont spray it anywhere that bees might be.
Cheers
JGM