It sounds like you're doing everything right. For leakage, use the freezer bags instead of the regular thin zip-locs. I've only had them "explode" on occasion, and I've probably fed thousands of times by now. Also, I'm not sure what type of tongs you use, but I have used 18" hemostats for years with great results.

There are definitely pros and cons to every feeder type. My personal preference is Pre-Killed, but it's not cost-effective with only a couple of snakes.