Easier to find a few strong men at your destination to help lift it out, with your setup you would also need to take the engine or ceiling cranes with you to get it off the trolly. Neither type of trolly would run well on grass anyway, particularly if wet.
A fold up wheelchair type ramp would be better to get it out of the car and onto the rally field. I've loaded the Fowler a couple of times myself with a ramp from a bit of ply with support in the middle, put it in low gear and turn the flywheel by hand to drive it up. Don't stand behind it though should it slip. Small ratchet winch would probably be a safer bet.
