Basically, as long as you don't use too much H2O and you have your RP and iodine in a suitable vessel that's being heated properly... the cook is likely to work. That's assuming you don't have other rubbish in it that screws everything up; after the cook itself, you just need to extract the meth and attach the hydrochloride salt to get your methamphetamine hydrochloride. Really the hard part is getting the materials and knowing what to do with glassware -- but again, I never actually went through the process.