Capacity is king. From 90% to 100% takes about 5 times as long (or so) as from 50-100%. So the bigger the bank, the more forgiving that way.
And there's Peukert to consider. The bigger the bank, the slower the draw on them per a given power consumption. The slower the draw, the greater the capacity per the given bank, i.e. if you pull 100A in one hour, your bank end up at 25%. But if you draw that same 100A in 20 hours, the bank might end up at 50%. These numbers are for illustration only, but the idea is true.
Also, it's been said already in this thread, but it's not ideal to have flooded batteries in the open air of your minivan. If that's your plan, then it wouldn't be a bad idea to invest in those AGMs. If it were me... I would. But then I kinda' want to see my kids grow up. That might be overstating it... a bit... but then... it might not.
I'd say chances are well below 50% that you'll have a problem with strapped-down, flooded, ACID batteries in the cab. The risks are only at their greatest when the batteries are under charge. That's when they outgas Hydrogen. The Germans were superb Zeppelin engineers. They gambled with Hydrogen too. Most days... they turned up aces. Not all.