Is there a specific silencer to use on an inland waterways craft for Webasto Thermo top C 5.2kw please? Also can this unit be ran using a standard domestic thermostat eg a simple Danfoss programmer?

for inland waterways vessels we would strongly recommend a marine specific silencer because they are designed to be gastight. For further info please review Webasto marine silencer and required accessories on our weblinks below

https://www.butlertechnik.com/item/Webasto/or-Eberspacher-Marine-Exhaust-Silencer-24mm-x-1800mm-9014067A-1322001A/5NO

+ required adapter and exhaust clamps, plus insulation if required

https://www.butlertechnik.com/item/Webasto/Air-Top-2000-heater-exhaust-adapter-22mm-to-24mm-92641A-1320382A/5NQ

https://www.butlertechnik.com/item/Eberspacher/or-Webasto-Heater-exhaust-clamp-for-24mm-or-22mm-exhaust-15261102-91383B/6T1

https://www.butlertechnik.com/item/Eberspacher/Webasto-or-Eberspacher-exhaust-lagging-insulation-40mm-11004-41V0001-Meter-Lengths/5IN

Regarding a controller? The Webasto Thermo TOP can be switched via a timer device that provides a switched 12v output, so yes tthere a a number of non-Webasto programmers that can provide this. Incidentally, Webasto do not recommend the heater is switched via a room temp device in addition - primarily due to increase likelihood of frequent cycling of heater