How do I convert my CASA CPL to Thai DCA CPL
 

I am a foriegn, only hav 300hrs, holding CPL/MECIR and ATPL ground subjects, What do I hav to do to convert my license to Thai DCA? Thanks

I take it by Foreign you mean you are not Thai?
You will have too approach Thai DCA for permission and they will
Most likely ask you why you want a CPL as for ATPL you wont get it.
Normally you get an ATPL validation for use at the Company who has offered you a Job using your Current ATPL. That allows you to operate a Thai reg Aircraft.
Basically If you dont have a Job Offer from Thai Company and hold
the requiaite experience you may find it almost impossible.
I did know one Farang who had CPL but they would not give him IR with it.
Hope that helps,,

get all document from your current license office (CASA) and go to contact Thai DCA office. If you are lucky enough you will meet helpful staff who will tell you the next step. If I am not wrong ,You will need to do some exam like airlaw.

Is it possible for a low hour expat pilot(<300hrs) to secure a job as an FO in thailand?Or do they require ATPL like in china?

In a word,no.

It's all about experience.

What are the benefits in working in Thailand anyways? what are some of the reasons you guys are working over there? I will approach a point where I have to decide whether to fly in Canada or go to Thailand. I do have the rights to work in both countries. I don't mean to bash, just curious.