I have the same tool box that I turned into my field box. Im basicly using the whole top part to tote my transmitter and starter and my tools on the removable tray.. As you can see i made a master switch which turns everything off and on. When i first built the fieldbox i noticed it was a pain to pull around in grass since it had like no ground clearance. So upon studying the orginal design how how the wheels were attached, i noticed i could just pull the whole wheel off. I pulled both wheels off and reversed how they fit in the slot. It then raised the box about another inch or so. Since the wheels were sitting higher i had to put some small "legs" in front which is screwed into the bottom.
Had lots of troulbe with the hobbico fuel pumps so i went to the junk yard and stole a windshield washer pump off an old 80's volvo. Which is also a geard pump like the pumps at the LHS so i can put fuel in and suck the fuel back out of the plane.