i had it on mine for a while - it helped as a wheelie bar sometimes, othertimes it just ensured the back wheels came off the ground and went over anyway... the sand on the beach would creep into it too, which didnt help much. also the lid had a tendancy to get ripped off through wheelies! lol - its not as bad as it sounds, but its not a perfect solution.

some heavy duty tape around the box to help hold the lid on would be a good plan tho. taller gearing is good too, its too much of a handfull on stock gears imo. doing both should calm down the wheelies, and open up the chassis a bit.