So are you looking for a Diesel heater for permanent installation in your rig?
Next question would be what kind of heater you are looking for. Water- or Air Heater? Do you want to warm up your cabin for living/ sleeping in the rig. Or are you looking for a diesel heater to heat up you engine coolant in cold winterly conditions independently form a power souce which is needed for the 230/ 110V electric heaters?
I am not aware of the market in the US. With regard to manufacturers, here in Europe, we have several players in the market. Beside the well known top dogs Eberspaecher and Webasto there are also others since some time. For example Autoterm, formerly known as Planar has become popular in the offroad and vanlife segment and is a bit cheaper than the other two. A sometimes overlooked manufacturer is the finish company WALLAS. They are known from the boat and yacht sector and have products also interesting for overlanders. Beside that we have some other comparable cheap brands. And of course there are some very cheap chinese products on the market.
Personally I have made very good experiences with Webasto and Eberspaecher. A bit more expensive as the cheaper once of course, but good quality, reliable, userfriendly operation and spareparts easily available if necessary.
Depends on the country / region but here in Europe it is also important that the heaters have the necessary approvals to be streetlegal. So this might be a point to be taken into consideration.
Please read also the
Diesel Heater Exhaust Recommendations by @Polaris Overland here before or when installing a diesel heater.