I would go with a Propex, they are very quiet outside the van whilst an Eber sounds like a mini turbine (especially if you haven’t bought a silencer…I have one on my work van). If you are a light sleeper I would install the propex away from the bed, as the blown air noise can be enough to wake you up, I reckon a Y piece so there are two outlets would reduce the noise considerably. Controller near the bed, obviously!
I was watching for second hand but ended up buying brand new, I think a tatty old one was £300 from ebay, versus brand new with all the fittings for £420. And unlike a woodburner, they are completely safe as room sealed.
I have an LPG tank which is another big ticket item, but you could consider a Gaslow style refillable bottle, benefits are cheap LPG from petrol stations, and crucially, only need one tank as you don’t need to empty it, swap over to the spare and then exchange the empty. You would just need to budget for the fill point as filling stations don’t like you filling at the bottle directly, as the travellers have dodgy adaptors to allow standard propane bottles to be refilled from the pump which is very dangerous as they have no protection against being overfilled.