If you want to stay with the look of the step tank then you are back to a custom unit or modifying the tank itself which may be your best shot. I have successfully welded gas tanks like these and it can be done but is tricky. I'd check out the local welding shop and find one who understands the risk but will take it. I use to flush them with water for at least 30 minutes and then fill them completely to get all the air out. They would sometimes still catch fire but not blow up.
I'll hang onto the crane unit until you win the lottery (or I do
). Good Luck David.
