First - your son needs to get the new ork codex where looted bassies aren't an option. There's plenty in the new ork codex to make up for it though.
Secondly - drop the lith in 1000 points. Bulk up with more warriors. Warrior units of 19 are a real pain in the ass for me to kill with orks when the lord is nearby with an orb. I assualt, kill a few (doesn't matter if the
pk nob does or not because the orb is nearby), 2/3 of what I killed gets back up, the lord veils them out of combat but within rapid fire range and I lose a substantial portion of the mob. Throw in 2 small units of destroyers and you should be able to counter what he throws out you.
Gah, I hate giving crons advice...
(
btw, you are not playing the ordnance correctly - place template, roll for scatter (using
2d6 pick the highest since it's out of
LOS), if hole is still over model, roll
2d6 (
pick highest) for
AP add to S, if glance or pen then roll on appropriate chart, if a pen roll on ord chart, not pen chart.)
EDIT: thanks to AnStWe for the catching my error.