The really critical step is the first developer (E6) or developer (C41 and RA4). You can usually manage to get the developer to some known high temperature before you use it, at least for a few minutes. The instructions for the original Mitchell Unidrum (same as Beseler, but a bit earlier) included a chart for the drift through method for processing prints. If you know the room temperature and the development time, you could look up a starting temperature for the developer that would produce good results as the developer cooled down and drifted through the target temperature while you developed at room temperature. You usually started at something like 104 (for 100 F processes) or 77 (for 75 F processes). The idea would probably still work for film and prints, but you might have to do some experimenting to determine the right starting temperature. The other solutions all work to completion and are less critical for temperature. Plus or minus 2C is usually OK. It is pretty easy to build a solution warmer to keep solutions at a elevated temperature. Start with a container that will hold the bottles with some room to spare (fish tank?) and use a fish tank heater with a built in thermostat to maintain the temperature. It works quite well.