You could build a "cubbie" for it for the back of the truck. That way the dog could have a space on the roof of the cubbie.
I had a large tote as well, but ended up scaling down because of storage and weight
when it was full.
I have scaled down to a 2 gallon kitty litter container. I make more trips, but it is easier to handle and not all that big a deal. I empty when I feel the need or have the time.
It would take a year to fill 25 gallons!