Hi HK,
I had a quick look at some sources and it is said Dupont lost all his ambulance caissons in the 1805 campaign. This is logical: Dupont famously lost all his train at Haslach. However, it does mean they at least had some caissons dedicated for the medical services.
This actually raises a question. I was impressed the 9th only lost three men dying of wounds. I supposed the medical services were organised, but clearly they would have had none of their supplies at the end of the battle. All the more remarkable they coped with so many wounded men. I need more time to interogate the source, but the 9th's surgeon major in 1806 appears to be asking for medical equipment to be mounted on horses because the caissons went missing in the previous campaign. In any case, a letter from September 1806 is still talking about 1 four-wheeled ambulance caisson per regiment with a small corps level reserve. Certainly no mention of special wagons to evacuate the wounded.
Terry