I had always thought that you feed 15% bodyweight. But it seems more and more I am reading that people are feeding 80 - 100 gram rat per week even for the biggest balls. This would mean than a 2000 gram snake would eat 100 gram rat which is 5% only?
If that is the size of prey then I don't see what the problem is with mousers then because I can easily just feed 2 jumbo mice that are about 40 - 45 grams each and it would cost the same as a 80 - 100 gram rat, at least according to my rodent sources' prices. I find that balls much more readily take mice than rats and if it only takes that small volume of food then I don't see why not just feed them mice.