It's almost impossible to keep the flying insects out during the day when people are coming and going. A trick my late wife and I learned when we lived in Somalia, though (mosquitos carrying malaria were the risk there), was to keep a can of pyrethrin insect spray handy. After you're in and the doors are closed, do a quick spray around the top of the walls (where the wall meets the ceiling). The mist will drift down and kill insect on contact. (Also works for mosquito netting tucked in around the bed.) Mosquitos tend to gravitate toward the vertical surfaces and pyrethrins are considered nontoxic to people and pets.