Who would know if you work from a home office? And if you're really scared of being snooped by Thai immigration, you could use a VPN. Personally, I doubt Thailand cares very much - at least for now. Anyways, with that kind of income it's easy enough to build a nice early pension quickly, provided one doesn't spent too much each month.
I work remotely as well and also for a US company as freelancer, but at the moment that equals only ~6.400 USD per month when working full-time (40 hours). I have to improve my negotiation technique somewhat it seems. Still it's plenty to live here and build some savings of course.