You should get your TV 60days /90days one before arrival, save all your trouble or risk of getting rejected at check in or upon arrival in Thailand. Get the right Visa, save yourself the trouble. You still have time, if your trip is in August.
I think If you dressed not sloppy and scruffy and be presentable, usually not a problem. Have a friend that lived in BKK on VOA exempt, flying in and out of BKK only for the past 10 years without a problem. He carries his house book with him. He is from Singapore.