In the current issue of Coastal Living magazine there is an article describing a trip Jaime Shannon from Commander's Palace and Johnny Earls from Criolla's in Grayton Beach, FL took through Louisiana to Cajun country, stopping at some fabulous places for seafood. I think you might find it interesting and perhaps helpful for planning at least part of your trip.
As you pass through Houston, you will see several branches of the Taqueria Arandas chain off the I-10. The food is wonderful, authentic Mexican immigrant stuff. Arandas also has seafood restaurants, the "El Siete Mares" type of places, also fabulous. After you pass downtown Houston, watch on the north side of the interstate and you will see both an Arandas taqueria and an Arandas seafood restaurant.
Not sure if it's on your way (sorry, my geographic knowledge of that area isn't great), but very under-mentioned on these boards and elsewhere: Robin's (pronounced, of course, ro-BANS) in Henderson, LA (3082282725).
It's a relatively upscale place, and their crawfish can't be beat, especially in etoufee. the owner's a real character. great wine list, too (they have a wine spectator award sitting around somewhere).
give a call to make sure they're still in business, it's been a few years