The base itself is fine and I've seen no noticeable settling thus far. That being said, despite my best efforts, the tub is not completely 100% level but it's pretty darn close. If I had to do it over again I would use a powered compactor to compact the base - I didn't have an easy way to transport a rental compactor so I tamped everything with a hand tamp. The last layer of stone dust probably was not as compacted as it could have been, and when they slid the tub onto the base during delivery it did scrape off some small amount of dust. It's not out of level enough to cause any issues so not really a big deal.
It's not rained here yet since I had the tub installed but I don't really expect that to cause any issues either. The tub covers all but a couple inches of the base on all 4 sides.