Yikes! great pictures good to see you both out cleaning but that tank? I wouldn't want to sit in front of that particularly because of it's height, it's going to be pretty unstable. I carry 650ltr in a flat tank and it's strapped to the chassis with the biggest straps i could find. Seriously i would look into changing that especially if you carry your little one in the front too. Wouldn't cost too much really.
It is a water butt , But it is baffled, The frame that goes around the tank is bolted down to the vans chasis and the straps pull it down.. As for the height, well there are window cleaner companies that use 1000 litre tanks and they seem fine..
About 3 months ago I had to do an emergency stop, Now everthing went flying ( Tools, Cds Toolbox ) but the tank did not move a inch and I mean An emergency stop
..
But why take the risk I will have the tank looked at and thank everyone for they concern for me and my family
Glyn
Will be off line now untill tomorrow
Thanks