I used the County Line carryall several years ago as a model for making my own design.
I could not find any of my pictures before I started adding on the additional items so the one below has the sprayer boom attached.
I found that I could build the carryall for significantly less than I could buy it (if I discounted my own time)
I also built my own boom sprayer (with modifications) based on the design of Fimco but I thought my design was better so did it. (Also cheaper if I discounted my own time)
I had the concept that I would use my carryall for multiple tasks so I designed it for all the "add-ons" that I could imagine. I have never removed the sprayer from it however. I put a much larger tank on it than any that manufacturer had until you got really, really expensive.