It's possible to do RA-4 processing at significantly lower temperatures than the 38C you mention. Some (non-Kodak) RA-4 kits are explicitly designed for this, with ~1-minute development times at room temperature (say, 20-25C). The last I checked, the kits that are marketed for this type of use are a bit pricier than their 38C competitors. Even standard RA-4 developers, such as Kodak's, can be used at room temperature, but you'll need to extend the development time, probably to the 2-3 minute range depending on the exact temperature. I'm not positive, but it's possible some filtration changes would be needed, compared to using them at 38C. FWIW, I've never bothered raising the temperature of my RA-4 developer and I'm perfectly happy with my results. I've used two or three different brands of commercial kits and at least one mix-it-yourself formula. Depending on the season, the temperature in my darkroom ranges from 20-30C. I adjust the developing time accordingly.