this might be a good way to go. biggest drawback I can see is that I would need a big water heater instead of an instant water heater. wondering if maybe I should get a slightly longer trailer to accommodate a utility room which has this big water heater and maybe some sort of greywater filters or treatment tanks as necessary. it would be great to be able to treat/filter greywater and then reuse it to supply the radiant floor heat but this open direct system requires the water to be potable (as it is going to both faucets and floor) and most greywater treatments do not result in potable water, from my understanding.
source: http://www.radiantec.com/pdf/Radiant_Heat_Design_and_Construction.pdf
source: http://www.radiantec.com/pdf/Radiant_Heat_Design_and_Construction.pdf