I know a couple of people who have tried to grow dahlias here in FL. They both said it was a constant fight with insects and fungal disease, and they both gave up after one year. If your summers had fairly low humidity, you may do ok with them, but I just looked up Port Arthur, you're pretty humid there in summer. (I sailed a regatta in Houston in July once . . . whoa, hot!)
Another way to find out is to ask your neighbors. If there's someone with a great looking garden nearby, see what they say.
We also do have a forum specifically for Dahlias, so you might ask the folks over there if any of them grow in humid places.
