I am about 90% finished installing an Espar D2 in my FWC Hawk shell Monday. The camper came with the stock Attwood propane furnace installed, which I immediately came to dislike. I ripped out the original furnace, and mounted the heater inside the same cabinet. I'll have to make a new outside access panel as I don't want to cut up the original one. I chose to plumb a separate tank so that I can use kerosene instead of road diesel, and for now avoid making any changes to my truck fuel system. I did a couple short test runs of the D2 to make sure things worked, then spent the night in the camper with overnight low temp about 11 deg F outside. I found the D2's performance acceptable in all ways, but it wasn't the completely perfect experience some people seem to report (not referring to anyone in this thread! I read hundreds of reviews before pulling the trigger). Supposedly the new D2s have much quieter fuel pumps. I've never heard another one, and mine is definitely noticeable but I'll have no trouble sleeping through it. Also, supposedly the new controllers (or maybe the new optional upgrade controllers?) have some altitude compensating function good up to about 9000ft or 9900ft. I can say firsthand that it seems to work just fine at about 700ft in my driveway.
Everything is a tradeoff so to each their own, but here's a little of my perspective:
Things I like:
+Single fuel source if needed (diesel truck) - although I'm going to try to run kerosene in the heater for now.
+No more propane required for my camper.
+Much more energy-dense fuel, so I can keep a lot more fuel onboard in the same volume of storage space.
+High heat output.
+Much smaller physical dimensions.
+German engineering, especially in the controller which is what I will interact with the most. Apparently this can be a pro or con but I like the look/feel/sense of quality.
+Lower electrical draw than the original.
Things I dislike:
-Very expensive, especially considering it replaces something that nominally does the exact same thing.
-The Espar kit is great but I'll end up spending even more to finish the install the way I want it (separate fuel tank, heat control stuff for the exhaust, modifications to the cabinet, etc).
-Kind of loud. I don't have the muffler hooked up yet, but the combustion intake is actually pretty loud, even before ignition happens. Probably a little louder than the stock heater in a couple different ways.
-The exhaust is very very hot. I am keeping the heater inside the inside cabinets, but I am realizing the exhaust contacting flammable things inside is a significant safety risk that will have to be addressed.