when we ran sr champ kart, we had to bolt on roughly 120lb. i started by using 2 plastic fuel tanks mounted on the floor pan and filled with water. the rest went on with the kart and driver on the scales so we could get the percentages the same. when we had the kart built i asked for 4 flat plates to be welded on the frame so weight could be added. the whole procedure was a pain in the ass but the weight was where we wanted it and installed safely. the rules said the weight had to be bolted on with either double nuts or cotter pins. i used nyloc nuts and safety pin type cotters. as far as the weight being painted white....the main reason is that if it falls off, it can be easily spotted on the track. the tracks we raced at took it a step further and made you paint your kart number on it. if they found it on the track, you were DQed from that race and had to get teched before you went out again. ps.....sheet led was legal but it had to be bolted in the seat.