Running a Chinese 5kw unit (Vevor branded) for a couple of years now and it's been solid once I sorted out the initial setup. The main thing most people don't do right off the bat is the glow plug — it's the weak link on all of these. First sign of extended cranking before ignition, pull it and check it. They go fast if you're running cold starts in single digits. Glow Plug & Gasket kit is $12 on Ebay. Bought and keep with the Heater - Cheap Insurance.
The other thing that'll save you headaches: prime the fuel line before your first cold start of a trip. Run it on low for a couple minutes before you actually need heat. Diesel gels in the line faster than you expect when it's been sitting, especially if you let it run dry last time out. Messed with the Non Gelling Additive? Good Point!
For mounting — I've got mine inside the cargo area on a steel plate with vibration isolating mounts. The exhaust routes out through a grommet in the floor. Keeps all the noise outside but I can still hear it cycling if I listen for it. Running the intake inside the vehicle versus outside makes a noticeable difference in ignition reliability in cold temps. Guys are Using these Ice Fishing and Outside their Shops in Saskatchewan & AK. I've never had any Start Issues, Unit is 2 Years old.
For a trailer/RTT setup, mount it under the trailer if you can. Keeps the weight low, keeps the exhaust clear of your living space, and you don't lose interior room. Under Trailer is Very Dirty (Rain Mist) but maybe tucked in a Cubby would be Best. I have not had to Open mine but others have.