Trang is a lovely quiet clean town with awesome seafood,dimsum,trang cakes and cold coffee pronounced Ko Pee to die for.
Breath taking waterfalls and the amazing Dragon Cave.
You have a better choice to rent a car in Phuket or Krabi or Hatyai then Trang.
Furthermore the train ride from Bangkok to Trang is long.With Airasia fares as low as train i suggest you fly from Bangkok to Phuket or Krabi or even Hatyai and start from there.
National rental had a deal of 500 baht per day including insurance if you hired for 30 days.Rent the car or pickup at airport or book in advance.
I had written a write up last year on Trang so if anyone wants it they can email me on firstname.lastname@example.org
In addition to the thing mentioned above, I would also like to say that it can be very interesting and exciting to feel droplets of water laced with carbonate dripping on you as you walk through some of the caves.
I am at a loss for words what to describe this adventure - in a way it reminds me of my Blue Grotto trip when I was in the island of Capri in southern Italy - the only difference is that this Trang cavern adventure lasted much longer and went through more adventurous routes.
One thing I like about this activity is that you can get the opportunity to stop at designated stops to explore certain caves in further details before you get back on the little boat to continue your tour.