I should mention here an excellent website and the ongoing research presented there by Ms. Joanna Dowling. www.restareahistory.org.
Ms. Dowling is an historical architect and a fellow devotee of the roadside park. If you are interested in not only some Texas sites, but parks in other states, historical and architectural information plus loads of links, please check out this website. For more information email: firstname.lastname@example.org.
Not long ago, Ms Dowling mentioned wanting to do a Texas specific feature on her website sometime soon. I am certainly looking forward to that opportunity to assist.