A repo man (now known as a "recovery agent") is not permitted to "breach the peace" in Texas in effecting a repossession. They are allowed to use "self-help" repossession, only if they can do so without breaching the peace. Breaking into a locked garage would clearly be a breach of the peace, and in my opinion would subject the recovery agent and possibly also the finance company to civil liability (a lawsuit from you), and may also subject the recovery agent to criminal liability.
However, if you continue to hide the vehicle, the finance company may file a lawsuit and obtain a writ of sequestration from a judge, which is basically an order to a sheriff to "arrest" the vehicle. In that event, if the sheriff knew the car was in your garage, they likely could legally break in and seize the vehicle, as they would be acting pursuant to a court order.
I should warn you that it can be a felony under the Texas Penal Code Sec. 32.33 to conceal property from a lienholder with the intent to hinder enforcement of a security interest. I strongly suggest you consult an attorney concerning your actions and possibly re-think your strategy of locking up the car until you make payments. It could land you in the "hoosegow."
My law firm is a debt relief agency and I help people file bankruptcy.