Want to see the country not the cities

You can do that if take private tour and request them to arrange what you want to see, local agent can help. We booked Halong and some tours with Indochina Best Travel, they offered good price. You may contact them to customize tour as your request.

In Cambodia only a few country areas have small scale tourism, these are like Chi Phat, where they have homestays, from what I heard. All the others are pure Cambodian areas, which are extremely poor. You can easily go to any of these by hiring a tuk tuk for a day or renting a motorbike from a nearby city, there are no organized tours to see these places. I would imagine Vietnam is the same.

Forum please stop mis-information it helps no one just because you are unaware of something it does not mean it does not exist

There are several tour companies in Cambodia that take you through the countryside - some by bicycle some by motor bike and others by car/van so as usual you are providing wrong information. There are also companies that will tailor make a trip to your specifications

I do not know the names of these companies (apart from spice roads who do tours by bike)but I see them coming through Chi Phat and know some of the guides. I could ask around but I am sure a search of the internet will yield names of companies that do this sort of thing

I should imagine it would be easier in Vietnam to plan an itinerary, travel independently then arrange tours locally.

I'm not providing misinformation, apparently you misunderstood what I said, I said a few country places are prepared for tourism, and the rest are pure Cambodian areas, this is completely true. I also said it's very easy to drive around in any of these areas, by yourself, or with a tuk tuk. In case you don't know tuk tuk drivers are often also tour guides and will be more than happy to take OP on a country trip anywhere.
As you say there may also be tours, but even you only have unclear information about these tours, which may or may not exist to the place the OP wants to go, or may be highly seasonal and not exist at all at the time the OP goes. On the other hand a tuk tuk is something you can always count on.

Timescale? Being a linear country Viet Nam is easily traveled without a tour group. You could use the rail system for coastal. Or travel by bus along the H14 for places like the wonderful Kon Tum.

Sometimes you dont want to travel straight up or down a country but in a loop. I'd rather do the loop, myself.

the thing about getting off the beaten track is to get away from the places geared up for the tourist

The reason I have unclear info is because I am not in the target market I am more than happy to go off and explore and be the only "white" man in the village and do my own exploration. (I have just returned from 2 months in Tanzania and with the exception of the beginning and end of the trip I saw no other tourists)

IMPOSSIBLE to answer for Vietnam unless we know how many days you plan to be in that country; transports are very slow (35 km/h average including trains) and the country is not wide, but very long (Saigon-Hanoi 1720 km)