Tie-Downs - Etrack, 2 levels
Tie-Downs - Recessed floor D-Rings
Tie-Downs - Extras of both kinds.
Get them on the walls.
Get them on the floors.
When you think you have enough tie-downs, Double it.
After that, add some extra tie-downs.
Then, make sure that you get QUALITY ratchet straps and make sure your people know how to use them.
Do NOT use bungee cords - those are great for holding groceries in the back of your car, not securing a 350lb mixer cart travelling at 75mph in your trailer.
GET VENTILATION - Ceiling vent, fan, anything.
TX Summers are hot. Trailers are metal boxes, remarkably similar to a large oven on wheels.
You may want to get a few extra tie-downs