In most of the SEA countries, you can easily leave the country for one or two days and return and receive a renewed visa on arrival. Many companies exist within each country, and will basically hold your hand through the whole process and make it a bit more convenient (it does cost a bit). Keep in mind, if you constantly do this in one country (Thailand for example), they make begin to ask questions about how you are affording the travel and why you keep returning. This would only normally happen if you're returning to the same country for the 5th time in the same year for example.
So for the most part, you should be fine! Specific countries might vary a bit, so it's always best to ask these types of questions / do research on a per country basis. Hope this helps!