[Ulladh]

To complete the state title transfer you may be required to pay the sales tax anyway, unless you can document the vessel is going to be exported to another state or out of the country within certain time limits.
So you will at least pay state sales tax.

Keep the boat at a Texas slip, same as any other state, you will need a registration sticker (other requirements for USCG documented). The marina if it has its act together may also require current registration.

Leave US water and the boat and you may be subject to Canadian rules. Re-enter US waters you must report to a port of entry and show that you and your crew have correct documentation to enter, and that the boat has correct documentation.