Wait...you have a "couple" of 350 gallon units carried by a "1 ton" (3500 or F 350...right)? So, that is 5800 lbs of water, plus the weight of the sprayer (700lbs???). Aren't most "one tons" rated for around 4500lbs total payload capacity?
If you want to go bigger, I think you need to start with a bigger truck!
There is a company around here that has their units in an enclosed trailer. That is a nice option as it allows for more capacity than a truck could take and it is easy to drop the trailer at the shop and be on to the next task with the same truck.
I am not sure I could spray through 700 gallons a day with most of what I am doing. For the rare day I would, refilling would be a better option for me.
What are most of your treatments?