bucking it is using an air hammer with a a cup shaped bit to fit over the rivet head. They can be bought from places like Byler Rivet in Dallas or you can make one by cutting off a broken chisel and making a concave to fit the rivet head. The anvil can be any solid piece of metal from an anvil to an old brake cam and using the cam as a pistol grip to hold it. I have about 30 aluminum trailers and we do all repairs ourselves. Of course aluminum rivets are soft enough that they do not need heating. Probably an easy "shade tree" way would be to find a piece of iron on which the assembly could be laid for an anvil. Then anything like an old carriage bolt could be ground concave to fit over the rivet head. Then put the red hot rivet in the hole with a pair of tongs and set or "buck" it by hitting the tool with a hammer. The purpose of buck rivets is to expand inside the hole and the part that sticks out really doesn't have to be "smushed" that much. It won't fall out. The strength is from the rivet filling the entire hole. On the spring clamps, it's probably not critical, but if you ever want to rivet a cross member with hot rivets, it is very important.
