One properly sized prey item a week is PLENTY. Western diamond-backs that eat at that rate will grow to over a meter in length in about 18 months, and can reproduce at the age of two years. Your snake may not be obese yet, but if you powerfeed him and grow him as fast as possible, he will become so. Also, when you say you "handle him", are you saying that you aren't using the proper safety equipment (ie. hooks/tongs)?! I certainly hope you aren't free handling your rattlesnake!