I have a Webasto Airtop 2000. One of the reasons I bought my cheapie campervan was cos it came with this fitted.
I decided to move it last xmas to the rear service area and out of the habitat area in a bit of a remodel, and decided to Decoke it as it wasnt firing up every time and seemed not as hot as it should get.
Like nbrown said... as long as the main pcb electrics are working the rest of it is pretty simple a blower fan and motor rear section connects to a large heatsink with an injector nozzle and a glow plug. The fuel dosing pump which pulses to inject the fuel is external. I decoked the gauze and gave it a blast with a
Propane torch to clean it, put it back together and it worked a treat. Similar performance to a decent fan heater, so it warms up our hitop LDV converted job in no time even though its only rated at 2kw. Great bit of kit.
Yes they can appear a bit noisy.... but some of this is I think down to positioning. Mine was installed under the sofa bed so right under your head if you were lying in bed, so you were right over the blower motor, and also the air intake and exhaust below the floor as well as the dosing pump. So not a good site even if it was easy to put it there IMO.
Mine now is out the back storage area behing an insulated partition wall, and in a chamber so it can still draw air from the habitat space through a wall vent and from the under sink cupboards in the galley and a space behind them and the sofa/bed where it used to be sited, then runs the air through the heater and blows it back into the hab area. This takes away some of the operating noise and esp once it slows the blower motor after the initial warm up its pretty quiet. Also the dosing pump can clunk audibly... I found this was due to the operation transmitting through the chassis. It does have a rubber surround on its mounting bracket, but its not enough. When I moved mine I added an extra anti vibration mount and it made quite a difference. Plus its now mounted to the towbar bracket so as far away from the main hab and sleeping area (our bed is across the van and behind the cab swivel seats) as possible.
Btw I run mine off its own Small tank and run Kerosene heating oil through it. This is cleaner than red diesel and cheap siphoned out of my house ch supply. Webasto seems to run nicer and hotter off kero, and should burn cleaner and coke up less on kero too if some maintenance and running tips gleaned through web searching are right. Makes sense though.
Overall a great bit of kit. Once you've pulled one apart you do wonder though why they cost so much new, cos they arent complex and sophisticated tech. Mind you mine is an oldie and still works so they must be well made and pretty robust.