Yes, it’s possible.
After you graduate YTTC you can do your volunteering and internship at the same time.
You would need to arrange your own food and accommodation. There are plenty options in nearby areas. (Private bungalow for around 7000-10000 THB depending on season).
If you previously applied to volunteer with your YTTC and you are volunteering with us after your course, you can also book our budget friendly accommodation at the campus.