Yes and no...
In Penal Code 46.15, there is an exception to prosecution for PC 46.02 (Unlawful Carrying of Weapons) if the person is "traveling" (not just traveling salesmen). Traveling is not defined in the Penal Code, so it is left up to the courts to define it. Generally, case law has held that to be considered "traveling," one needs to cross at least two county lines and have an overnight stay. Generally. Courts have used looser and more restrictive standards for is legitimately considered "traveling." Also, local County Attorneys may have a stricter local standard, or may simply decline to prosecute becuase the whole issue is so ambiguous. Basically what I am saying is that the whole thing is a mess and there is no straight answer to your question.
Your best bet is to either carry a long gun in your vehicle (no restrictions) or get a CHL. Since Texas is a "shall-issue" CHL state, if you want to avoid any unecssary entanglements, I would just go the CHL route.