A year ago I stayed for 6 months. Due to the Washington DC Thai Embassy not coming through with the visa I paid for (lesson learned don’t use DC embassy) I received a visa on arrival, which at the time was good for 45 days. Within a couple weeks of entry I got a 30 day extension from the local immigration office. As I got close to the end of my 75 days I flew into Vientiane and got a 60 day tourist visa from the Thai embassy there. Then I got another 30 days from immigration. When I got close to the end of that I flew into Saigon and on returning to Thailand I got a 30 day visa on arrival which covered me through to my departure. For the trip to Laos I had to get a Lao visa prior to entry, I got it from their embassy in Bangkok. For Vietnam I got an e-visa ahead of time. I learned a few things along the way and feel more comfortable with long stays there now.