We use a precision temp 550. No change to propane piping needed. Was able to relocate line to fit new HW heater. Only issue I've had was running low on propane or low water flow due to a crap external regulator.
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'The Silver HamShack' (2007 International 22FB CCD 75th Aniversary model)
Multiple Yaesu Radios inside and many antennae sprouting from roof, ProPride hitch
2012 shortbed crewcab 4x4 Toyota Taco TV with more antennae on it