I've bred rainbow boas and I still have a few. Bear in mind that because rainbow boas are kept at a lower temperature than other boids, they digest more slowly, so an appropriately-sized feeder every 2-3 weeks is fine for a juvenile and my adults eat every four weeks. At an inch around I would be looking at feeding a smallish wean rat, jumbo mouse, or perhaps a very small rabbit pinky, every 2-3 weeks; something 20-25 grams.
A pinky mouse weekly isn't enough, that's what a neonate would eat.