So an update for you and others that may come across this thread. I play 1850p ITC rules, tonight I played a decent game but still lost (5-4). Here's a run down of my list and some information that might help to serve you.
2x HQ:
Big Mek w/ MFF
Painboy on Warbike
1x Elites
6x Nobz on bikes (half took
PK, other half took Big Choppa),
BP on boss nob, WAAAGH Banner for another guy
2x Troops
Gretchin (2 units of this)
2x Heavy Support
5x Lootas, 3x Meks (2 units of this)
Lords of War
Big Mek Stompa with Deff Kannon (just upgrade not swap for melee wpn), 3x Supa Rokkits
So this list uses
Ork Great Waaagh! Detachment so I can grab the Mega Force Field and Big Mek Stompa
LoW. The Big Mek is the warlord and is placed inside Big Mek Stompa along with both Heavy support units. This is your everything and unless you go against a 3x Imperial Knight ITC legal army, it's very tough and can withstand a lot of punishment (so far I haven't lost him). But he isn't immune to everything. Meltas are not your friend! The painboy on bike goes with nobz on bikes, and they are pretty tough but need to be used just right.
In my game tonight we rolled for ITC Mission 3
https://drive.google.com/file/d/0ByVzaY23LOX-VHVzei01Njk5d2s/view, and the board was setup from the last tournament so even. I used the Stompa to grab the Relic (you need to disembark a unit, have them grab it on your next turns movement, and put them back into the Stompa) and so remaining part of the game was me trying to table him while he gained Maelstrom points on me. The biggest draw back to this army through for ITC missions is the fact I don't have strong enough units to move around to hold or contest objectives. It's very fun, semi competitive but I think many lists will beat this or similar ones. Also key note for ITC, is if the opponents army does not have a
LoW (super heavy walker) for every hull point he does, he gains a maelstrom point.
Recap: Stompa needs to move as efficiently as possible to close the gap and shoot every single weapon during shooting. Also be aggressive with him, he can take a lot of punishment and only a few big guns may hurt him but you will gain back Hull Points every turn so no sweat!
I hope this helps a bit but keep posting on your updates or what you use to try with the stompa I'd love to see it!
-Raymond