Hi-Anyone know of a good Thai or otherwise housebuilder in Trang/Hua yai?

Could go and have a word with the ofice at Sri Trang estate - the houses there are very well constructed and the office might be able to point you in the right direction, they might even handle construction outside of the complex. Don't know a specific builder though, sorry.

Google 'house builder krabi'.

My recommendation is to steer away from farang builder unless you just want to spend more money. I have experience with this.