I always like the "rubber band" rule – the firer stands behind the battery and snaps a rubber band in the general direction of the enemy. ;)
More usefully, there are all sorts of stat's for new weapons in "The Sun Never Sets" campaign rules (available from TVAG), which is yet another reason to get the book, aside from its intrinsic value. The stat's relevant to the Zulu War are:
7lb Gun (less powerful than the 9lb assumed in the rules): 4 crew, 2 dice per figure, short/long range 18"/36", Class I to hit short/long 5/3, Class II 5/4, Class III 4/3, Class IV 3/2.
9lb Hales Rocket (used by the Naval Brigade): 2 crew, range 48", to hit (any) 5 (ground burst), 3 (air burst).
24lb Hales Rocket (I don't think it was used in Zululand, but useful info): 2 crew, range 48", to hit (any) 5 (ground burst), 3 (air burst).
Firing rockets involves a couple of steps. Designate the target normally, except that there is a 12" minimum range. Every 12" along the path, roll 1d20: 1-3 = 45 right for 1d6+6", 4-6 = 45 left for 1d6+6", 7 = 1d6" straight and explode in air, 8 = 1d6" straight and explode on ground, 9-20 = continue straight, test again.
If you manage to reach the target, roll 1d6, and evens = ground burst (3" burst radius), odds = ground burst (2" burst radius). Roll for every target in the blast zone.
If the rocket passes within 1" of any cavalry etc. or any native infantry, they must pass a critical morale test. However, the Zulus don't seem to have been very impressed with either artillery or rockets, so you might want to give them a +1.
Cheers,
Christopher
PS – one can make a passable rocket trough from a heliograph tripod and some brass wire.