What do you think: A 40 point mob of grotz inside a Battlewagon or Looted wagon manning the bolt on weapons.

Mobile firepower in a tough shell.
Four BS3 Rokkits
Grotz are cheap and expendable
Neat fluff and a myriad of modeling ideas
Grotz can jump out to claim home objective on the last turn if needed if you are sitting back and shooting with it

3x Kannons is much cheaper and has a good range anyways and can fire frag/krak shells
2 force organization spots vs 1 force organization spot for Big Gunz

If you went with this idea, what vehicle would you use, what main armament, and what upgrades would you give it?

Here are a couple of my thoughts (all options include a 40 point mob of 10 grotz and slaver):

'Beaky Basha'
Battlewagon with Killkannon and Kannon, 'ard case, riggers, and 4 Rokkits - 260
This one is easy - sit back and blast away. The riggers are there just to add an extra layer of protection in case they immobilize it so that in future turns another immobilized result doesn't take out a weapon. This has the possibility of wiping out a Marine squad every turn.

'Umie Krisper'
Looted Wagon w/ Skorcha, 'ard case, riggers, and 2 big shootas - 115 points
A nice cheap option to wreck havoc with horde armies such as Orks, Guard, or 'Nids.

'Da Deff Rolla of Deff'
Battlewagon w/ Kannon, Deff Rolla, 'ard case, riggers, 4 Rokkits/Big Shootas 200/220 points
Possibly the weakest of the options as the Deffrolla encourages moving 12" a turn while the kannon and bolt on weapons need a 6" move a turn in order to be useful. Perhaps use this kit out to support an infantry advance. Shoot any threatening targets on T1 and T2, and then once you are close, accelerate and start squishing things! Maybe use it to screen your troops or smaller vehicles and draw fire, or perhaps put it behind them to make it less of a threat until it's too late.

Anyone else have some ideas?