2000 Camry Malfunction Light

Hello, I have a 2000 Camry LE 4 CYL. with 220,000kms on it. Its a great car most of the time, but sometimes I want to take a hammer to it. Back in May, while on the highway, the engine light randomly turned on. When I reached my destination, I called Toyota to book an appointment to get it checked out...before the appointment actually occurred, the light shut off. So I canceled the appointment. fast forward a couple weeks and the light turns back on. It does this turn on, shut off thing many times, so finally its on and stays on. I get the car checked and they scan it and it gives an EVAP code. They said the gas cap was not holding tight and that I should replace it. I replaced it with a genuine Toyota part and everything was going fine until today, when the light turned back on. Should I be concerned? I have heard about the evaporator systems in these cars sucking and costing a pretty penny to fix...any help would be greatly appreciated!