Nope
I think the 'lootas in a battlewagon' strategy is a bad idea. The lootas are ironically safer in cover, since woods/ruins won't explode. To avoid the danger of blast/ordnance weapons, I like putting the lootas directly against the back of the deployment zone, so any blast/ordnance weapons aimed at them that scatter slightly away from them, but off the board, disappear completely. This isn't as effective in table quarter missions though, where 48in range isn't enough to reach everywhere.
In any case, it's not lootas, but 20 shoota boyz w/nob, powerklaw, bosspole, and 2 special weapons, that work very well in battlewagons. The wagon can move and the shootas can still fire. They're also great for claiming obectives, ramming enemy vehicles, and despite being shootas, they're still very good in the assault.
I'd never give a battlewagon more than 1 gun. Although it's tempting to load them up, if you move a single inch, then you'll only be able to fire one of them, so one is all you should give them. This is how I equip battlewagons (assuming they'll be a transport):
battlewagon w/one gun (usually a big shoota or kannon), grot riggers, and a deff rolla
Armor plates aren't really worth it, 'ard cases keep the units inside from being nearly as effective, and killkannons aren't effective enough for their cost.
If you want a really shooty unit, then don't use a battlewagon, use lootas, killa kans, rokkit buggies, warbikes, or deffkoptas. Battlewagons simply don't have the aim or number of shots to be effective. You're better off using a looted wagon with a big shoota, holding 5 burnas w/3 meks using big shootas. This gives you 4 big shootas and 2 flamer template attacks, for only 115 points, and you can still move and fire. A battlewagon with 4 big shootas and a kannon/lobba would not only cost a bit more, but it couldn't move and fire more than one weapon.