This assumes that your state doesn't require a title and you are in compliance with all the rules of your state
You have 2 options:
Sell the boat to them in your state, using whatever forms your state requires. Include a bill of sale detailing the boat. It would be nice if you included a copy of your registration, if your state requires it and some words in the bill of sale that say something like sold in the state of ...., no title is required nor exists and this bill of sale is proof of ownership and of the sales price of the boat. It seems to carry more weight if it is Notarized
When the boat gets to Texas they will have 20 days to register and title the boat. http://www.tpwd.state.tx.us/fishboat/boat/forms/
See form 143 and 504http://www.tpwd.state.tx.us/fishboa...and-or%20Registered%20Through%20TPWD.PDF
In the matrix in the link above includes boats that have no title.
If you are feeling real nice, have the new owners call Texas Parks and Wildlife either your local office or Austin:
1) Get the name of the person you are talking to
2) Tell them the truth, you are buying/have bought a boat in a state that does not require a title and you have bill of sale and whatever else
3) Ask them what you need to do to do
4) Do exactly what they said no matter how silly it seems it seems. They are a paramilitry organization, i.e. you can do what they want or keep doing it over and over again until you get it right.
5) Take all the paperwork to the Parks and Wildlife Office and say "soandso told me this is what I needed to do, here it is"
And help them with whatever Parks and Wildlife says they need.
Note not all Park and Wildlife Offices are equal and this is a state deal so you can use the one in the area with the best reputation, ask around. In Houston I recommend the one on the Southwest Freeway. Unless you have "friends" stay away from LaMarque
In general I would write up a separate bills of sale for the "boat", the trailer, and then everything else included (Sails any extras). This is because only the trailer and the "boat" is taxable.