I have helped install a Wallas in a Corbin 39 and was impressed with the low noise in general and the fuel pump wasn't audible. Some are installing them behind main cabin settees as that way the forward cabin area is not as far from the main unit. They are quiet enough that this isn't a problem. They have exhaust/intake fittings that are designed to be deck mounted if that is needed and they can be closed off with a twist and are waterproof when closed. Their power consumption is low - the 30D uses .8 to 1.8 amps @ 12 volts.
I have also been to an all day installation seminar given by the Wallas factory engineer. During the seminar a Wallas was running full time and couldn't be heard unless you were right beside it.
Other than that I have no connection to Wallas but if I was to purchase a diesel heater it would be a Wallas.