The 26 foot reefers certainly had truss rods when built, sans turnbuckles.
The 27 foot St Charles reefers, like the 27 foot UP built boxcars, don't appear to have had truss rods, but tension rods that ran the length of the car, hidden up next to the outer sides of the two center sills.
Derrell Poole has suggested that the 27 foot reefers were reinforced with truss rods when rebuilt in 1902-03, though I've never seen a photo of one.