Well, you may not like it, but the Mexican Army had no limbers for their guns. Everything was indeed hauled by oxen, but they were simply attached to the trails, or used a sort of "half limber" that had no trail case of ammunition, just two small wheels.
Their sole "horse artillery" battery did indeed have limbers, but they were the last usable ones from before the War of Independence. And they did NOT perform as "horse artillery" in the European sense. They simply were drawn by six-horse teams, also the last of their kind in the Mexican Army.
By providing limbers for your Mexican Army, you may be inviting the error of allowing them to move during battle. "Doctrine" was to have the guns moved up by their CIVILIAN ox drivers, sited prior to action, and then remain in place throughout. Only that last lonely "horse battery" could theoretically limber up and move after having been deployed.
The civilians hired to drive the ox-carts that served as battery wagons, and the guns, always made themselves and their "prime movers" scarce when battle was imminent. Just trying to find them and return to the battle would have been an impractical undertaking.
Once sited, Mexican guns could be trained and prolonged by their crews as one might expect.
If you don't already have it, you may wish to consider getting a copy of "The Mexican Soldier" by Joseph Hefter, a work that discusses all factors for the practices of that army, not to mention the primary source for all its uniforms.
Alternatively, "Gone To See The Elephant" provides full information on the strengths and limitations of the Mexican Army on the battlefield.
Both works are available as PDF's for economy.
TVAG
adds a tower to his 15mm trainyard.
