Here's what I have: Dodge 360, Holley 4bbl, Edelbrock intake, and Thorley headers. This is in a 1973 Dodge B300 RV. The engine lower end was rebuilt about 10k miles ago by a local engine shop (now closed). I have never towed anything and the engine runs smooth, quiet and strong.
Here's what is happening: Readied the RV for a short trip, changed oil and filter. After 575 miles checked the oil and it was down 1 1/2 quarts. Brought the oil up to full. After another 400 miles checked the oil again and it was down another 1 1/2 quarts. After another 200 miles and returning home checked the oil again, down another quart.
Here is what is observed: No oil leaks ANYWHERE. Plugs are not fouled. No oil in coolant. At cold start-up there is what I would consider a little too much white smoke coming from the right side exhaust. After warming up for a few minutes the smoke is gone.
So, where is all the oil going? I'm thinking most likely valve seals. But before tearing into the engine I'd like some input from those of you that know more about engines than I do.

 

What was done to the heads ? Was it re bored ? Leaking intake.. Lots of things can cause it to use oil.