I ummed and aahed for about 6 months over this to be fair..
Didn't find a secondhand one that was good enough, and all of them needed bits added ranging from cheap stuff like tubing through to silencers and the expensive bits like the timer..
In the end, I just went for it, thinking what am I doing paying this much for a heater, but I have to be honest I've never regretted it for a moment, and to me it has proved totally worth it, its made the van usable all year round, its my escape pod and through the whole winter I was regularly parked over the forest or down by the seafront for lengthy evenings with the heater on low and a coffee and a book.. I absolutely love it, it uses hardly any fuel, I didn't want gas so the the propex was ruled out, its quiet with the silencers so isn't going to annoy anyone else nearby, I would rate it as probably the best thing Ive done to the van. So much so, that if I started again, an Eber would be the very first thing I would do, even if it was the only thing I could afford to do, cos tbh if you're warm you can be comfortable in a sleeping regardless of how cold it is outside..