I think Hemi's are great for towing open trailers. I just towed a 1946 Power Wagon 600 miles on a 10,000 lb equipment trailer with a Hemi Durango. The Durango had 106k on the clock. Loaded trailer weight around 8600-8800 lbs. It got 13 MPG and change at 62 MPH with a headwind. Before I got into the headwind it was 14 and change.

Several folks have been dissapointed with performance on enclosed trailers in a headwind.

With 200k on the clock though I don't know. Even if the engine is fine what about the transmission? There are a lot of big ticket "if's" with that many miles.