For fun, we house rule that when you roll a ten and thus run out of ammo when firing artillery, you can re-roll if there is a caisson attached to the battery. We only have a couple per army so it adds thought to where we place them and encourages the addition of these great looking units to the tabletop.
I like the optional rule that an area ( 12" in 28 mm scale we use 6" in 15 mm) is an area of rough ground and use this for the limbers etc. As it makes the batteries more of an obstacle to troop maneuver and also give the option of a few dioramas ( when I get round to doing them!) on the battlefield