For pasture spraying I have a 300 gallon 3 pt, but some day, when I get a Round Too-It, I'm going to put it on a trailer. 300 gallons is a lot of weight and can easily flip on slopes if I have it raised to spray 18+".
For spot spraying the complete fence line, I have a gun on the 300 gallon that is the cat's meow for fences but for spot spraying small areas, I have a 15 gallon lawn and garden on a trailer with a battery powered pump. The wheels were too small for driving through pastures, so I put the biggest wheels I could find at TSC. They are the big cart wheels for square bale - manure carts.