BTW this is not limited to WP, I can also obtain BOI with no company prescence in Thaiand, this would be supported by the Hospital. Already spoken to BOI about this and it was their advice how to get it without a company here. They said may be possible through distributor but much easier through hospital where equipment is installed and maintained.
the distributor told me no need for wp it will be fine, no one checks, they have done this many times with installers from other countries working here but I told them as I live here I dont want to risk deportation and a fine and a ban, also not good for my company if caught working illegally and we are international company and it would prevent me entering other countries.Not worth the risk.
Basically the supporter, in my case a distributor, provides a supporting letter and invite letter but have to comply with same paper work requirements as if we were employed by them, those are found on the ministry of labour website, lots of company papers. In your case may be worth considerring BOI visa, no border bounces or 90 day reporting ;-)
so its not comparing apples to oranges, I have a valid work permit and based in Thailand living. The only issue is for next project in bangkok it will be different work permit as hospital location is different.
I live here and have a work permit. You do not need a work permit for machine repair, thats a specialist task exempt from a work permit. My work permit is to perform and manage installation activities and even to train others, for this I have a work permit and can extend if if I wish for the whole year or longer so it is not short term. If there are on going projects with no local skilled persons t perform the tasks you can do longer than one year.