After a bit of trial and error I've finally managed to make stock propeller engine which works well in a thin atmo on Duna, and at the same time it can provide enough thrust to allow creation of bigger airplanes. New engine is about 4 times more powerful than the old ones and it can be safely reloaded, which makes it reusable.
Duna Transporter is stock electric prop driven cargo plane designed specifically to be able carry 12t of cargo in thin Dunian atmosphere. RTG powered engines provide unlimited range and a maximum speed of 162m/s at low altitude and about 132m/s at 5k.
Link to the craft file on KerbalX https://kerbalx.com/Rade/Duna-Transporter