as stupid as this sounds, it sounds like you are describing an Eberspacher
gas heater. Noticeable characteristics of this beast are an exhaust pipe
down through the floor, and a metal tag w/ Eberspacher written on it. Are
you familiar w/ Eberspacher gas heaters? That green knob on your dashboard
w/ the white cross controls your gas heater. if you turn it, you will hear
this whirring sound that is the timer

>In the engine compartment of my '72 Westy there is a ~2.5 ft long
>black cylinder, 5" in diamter, with German writing all over it. It is
>in the upper left corner of the compartment, with what looks like an
>exhaust pipe dropping down thru the bottom of the compartment; on the
>back end is a white plastic cap with its own tube running up the side
>of the vehicle somewhere; a few wires running off it also.
>
>A friend took a wild ass guess that it was for the outlet inside. If
>not, how is 12V converted to [110v or 120v]?
>
>Please cc: to jeffs@almaden.ibm.com please, otherwise I won't see the
>answer until Monday - in digest mode.
>
> jeff
>---------------------------------------------------------------
>Jeff Schneiter........jeffs@almaden.ibm.com........408.927.1498
>If IBM and I have the same opinions, I have been here too long!
>'72 Westfalia                                             MA/WC
>---------------------------------------------------------------