i finally bought a plane, which I got yesterday. no way it will be together for this.
Shame that was going to be something I was going to heavily advice, despite my personal reservations against things like Flyers, Superheavies, D-Weapons and Fortifications (geese I'm practically a dinosaur in this game now).
The way I currently see it, with Orks our best bet to survive, and even thrive in the current 40k crazy is target saturation.
Don't get me wrong, I love my Footsloggers, but Footsloggers are pretty hard if not impossible to deal with some of the most recent releases. Which is great because we has Orks have lots of great cheap units and with a dual Force Org chart allowed in the Tourney, you absolutely have to take advantage of that!
That in mind I have some suggestions for your posted list, both in slight modification and possible additions you might want to think about, especially considering that you know you are going to go up against at minimum 1 Knight, and I think it's likely that you'll also see some of the Stronghold Assault goodies, if not a Strongpoint or Defense Network.
The Stompa and transporting Burna-mekboy squads. It took me a while to see why you'd take the Meks in the Burna squad, although I see it now, and by Mork and Gork I applaud you for such amazing tactical brilliance Warlord Argh! Since others reading this/commenting might not, here's why it's smart! The Ork FAQ has modified Mektools to replenish Hull Points. I know this might be old news for most, but it's new and big for me. Additionally in case you get some of its weapons bunged up you can Repair them. Oh and as an added caveat since Superheavy vehicles ignore Shaken results there's no downside if you roll the 1!
Now here's where I think you can improve the Stompa slightly though. You could switch the Burnas, with Lootas. Both units can take the Mekboys, both units would cost the same points, but I think you'd get a better value out of the Lootas shooting from the Firepoints than flame templates. Take that advice or not, you should consider what weapons the Mekboys have. While the KMB isn't bad, if you shoot them there's a chance you could loose your replenishing Hull Points, so I wouldn't KMB them at all.
You'll have to check the Big Mek's point cost or the wording, with just a KFF he's less than 100 pts.
Trukkboyz are a good way to go, but are they Shoota or Sluggaboyz? The Planks are a great addition drive by plinking of armor without having to actually assault is a major plus against a Knight.
The Deffrolla wagon is a lot of Ork players bread and butter. That said, it's still relatively weak in comparison to a Land Raider, and with the Forts and Lords of War your likely to see, I think the Deffrolla isn't going to be a great asset. Yes I could be completely wrong, but even with boxcars against a Superheavy walker that's Death or Glory-ing, your wagon will likely bite the dust, and seeing how it's about 1/8th of your army's points, I wouldn't recommend it. That's not to say it won't work, but that I think there's other options that might work better.
The Green Baron isn't bad, just suicidal. Suicidal isn't bad either, but the Green Baron lost his alpha strike since he can't assault when he comes on the scene, and I also don't think there's enough targets out there that will distract your opponent from netting a quick kill on the mosquito that is the Green Baron.
Biker bosses an Nob bikers are always great fun to play. But with a 4 man team you have to Ld check after a single casualty, and Orks aren't exactly known for their Ld value. Besides, being the only Bike squad in the army, to me it looks out of place.
All in all it's not a bad list, just one not fully optimized to take the full potential of the scenario. Case in point, this is a 2,500 point game where you get double Force Org! There's lots of goodies you can shove in when you've got double the standard Force Org, and I think many of your opponents are going to do the same.
Great Cheap Units I suggest taking multiples of...
With 6 Heavy Support slots at your disposal, amazing rules for artillery pieces, two fire modes, Ammo Runt rerolls, unbelievably reasonable point cost, and controlled by Grots for a higher than standard Ork BS; the Kannon really shines as tool in anyone's arsenal. As a side note, it is by far the Orks best Anti-vehicle and I wouldn't doubt it's usefulness against Superheavies.
I know you already have a couple units, but I don't think it's nearly enough for the purposes of scoring or even surviving till late game. If I was playing against this list, one of my personal priorities would be taking out your scoring units while trying to kite around the Stompa, and I think a lot of people would have a similar thought. Trukkboyz fast mobility, and can block of areas of escape around your Stompa, and hey you have a lot of Troop choices.
True they aren't my personal favorite thing in the world, but there's a great cheap choice for a Fort out there, and you have at least one of them, the Vengeance Weapon Battery. They're cheap, come for a 2 for one slot option, and with 2 Force Org Charts that means you could feasibly take 4.
I'm not saying you have to change your list, I'm just saying what I would do if I was playing in this tourney. Regardless on if or how you change your list, I wish you good luck.
Post Script: GAH Ninja-d!
I thought the same about Transports, but if you reread the Super Heavy Transport section in Escalation you'll see it. I'll admit to having to look very closely at it. As for the Burna squads, read my post and you'll see why its brilliant.