I'm about like all the rest so far as experience goes. I'll throw in my two bits because I do things a little different.
1. I polish to at least 600 grit. 800-1000 if it makes me feel better. I have done two barrels to less than that, and I am very very unhappy with them and will probably do them over one day. I like a shinier barrel, though they, in no way, shine like a hot-dip blue.
2. I will sometimes dilute my rust solution. I do not use Laurel Mt but I hear it is very agressive. I like something slow to match my schedule.
3. My schedule is such that I can usually do a boil in the morning before work and in the evening around dinner. Roughly 12 hrs apart. Because I don't want to risk pitting and because I like a better shine to my barrels than the "matte" look that some love and I hate, I do NOT use a hot box or raise the humidity. This works just fine in the dead of winter when humidity is unmeasurable, and in the summer when it is quite high. My basement or shop are both quite cool, which also slows the process.
4. I apply with a small BARELY DAMP cotton pad. The BARELY DAMP part is important for etching that very well polished barrel.
5. I plug my barrels with expandable neoprene plugs from the hardware store.
This works for me.
Brent