I am doing one response so as to avoid a sore typing finger.
airiding...you may have hit on the better way. My front bumper would take a bladder. I will look at that. I don't want a permanent 'box'. I have the correct tires for the E350..so, no..no big tires. But..my off road travels have been many.
Others...I am grateful for all the input. Thank you. Yes..it is tall and yes, it is maybe a tad top heavy. My vision saw/see's me watering before going off road, not driving around with a full 'bladder'. I asked the question...I shall investigate other options. A rear receiver is not an option. I have a bike box on the one that exists, now.
Someone mentioned Sharon reading my comments...you are kidding, right? You obviously don't know me. Sharon is the one person in my life that I will do most anything for. She supports me and accepts me...she loves 'docking and loves the deserts and wild places..the woman has no fears. So, if she needs more water than I currently carry, to wash her hair, to extend the stay...I will do what I can to provide.
Gary