Yes I think this method is ok. The crockpot usually brings the contents to a low simmer boil on low, and this is the recommended setting and works just fine for my cannabutter.
I think it's important to maintain a type of awareness about the simmer which I think you maintain just fine... it should be a low simmer not a heavy boil, you know the difference..
One thing that I learned from my trials and errors with making cannabutter is that the cook time very much does matter. I have always thought longer cook time is better but I no longer think that...
I think 24 hours is the sweet spot, because at this point all of the cannabinoids are extracted and further cooking only serves to degrade the cannabinoids.
I cannot contest to the science behind my assertion, but the results speak for themselves with my trials. I've cooked crockpots 30-50 hours and the longer I cook them the less the psychoactive effects kick in a good way, and the more the flavor becomes harsh.
I think cooking for too long burns off the active cannibinoids, so finding that sweet spot is essential, and I think that sweet spot is 20-30 hours. Not before or after.. that range is when you want to separate the contents.