SFO-HNL is a very easy RPU route. The 764 with lie flats is a particularly good use of an RPU. All year, not just "low season." UA is also currently flying a three-class 772 DEN-HNL; that's a nice RPU use as well.
My experience on ps has been quite different. I've not missed in the past two years. Though UA has made it more difficult recently with the change in policy about opening R at T-24.