We did a weekend not long ago, had fridge running on gas, lights on and off as usual (converted to LED) and 12V Ipod dock running, on the meter, battery didn't drop its 12V light. I was gonna add another battery, but probably won't worry about it. I have duals in my Prado and leave the 80L Waeco in there. Gonna try putting Waeco on Expanda battery to see how it copes. Also have to change wiring in Expanda to charge the battery while driving.
I would stick to using similar sized batterys in parallel too! As the batteries try to equalise between each other I would wire them up so that the Setec positive goes to the + of battery one and thenegative to the - of battery two. Then make you connections between the two. Not sure why this makes a difference, but everything I have read and seen during my trade and looking on the net, this is how it is done. Apparently make the two batteries behave as one rather thatn two connected which will cause the first in line to have a much shorter lifespan than the other.
Hope this helps!