Turns out I cannot get three drain pipes through the floor joist space (without major surgery) so am going to run them against the underneath of the floor joists in an unheated crawl space with one side open to the elements. I will insulate the pipes with foam wrap, and maybe even box them out ..... any other clever suggestions? Was thinking about using one of those cable style copper pipe heaters, but not sure if they'd get too hot for PVC. I have a standby generator, so the chances of protracted power loss is small, but the return pump could fail. I do keep an apex temperature probe in the crawl space because my chiller is in there, so could also run a space heater should the return pump flow meter read zero.