Condensation is a by-product of using propane heaters in an enclosed space. Much water/humidity is produced.
I am very interested in installing a diesel and/or gas heater in my FWC also and would like to learn more about the carbon build up/soot issues. From my reading it sounds like using the correct sized unit for an application along with proper installation and maintenance are keys to successful use.
Correct size - I recall reading somewhere that with these types of heaters it is better to have a slightly undersized unit that burns longer compared to an oversized unit that burns for short periods. I wish they provided more information on this subject although some companies do speak in generalities such as this is appropriate for a truck/van or mid-sized RV or larger applications, etc.
Proper installation - intake and exhaust length and angles seem to be important. From what I have read a shorter and straighter intake and exhaust are preferred while going longer increases maintenance. This make sense since the longer lengths can be associated with more restriction and a richer mixture.
Maintenance - somewhere I read that white smoke on start up is an indicator that maintenance is required while continuous while smoke is an indication that maintenance is long overdue.
It has been my experience with many other wonderful machines that if they are not properly sized, installed and maintained there will be unexpected problems. Germans, Swiss, etc. are know for their strict attention to detail, following instructions, etc. so it is my theory that many of the problem we read about on forums are associated with improper sizing, installation or maintenance. I am going to purchase one myself since burning propane which converts into carbon monoxide is not ideal for my application. I just need to select the ideal size and install it correctly in a location where I can easily maintain it.