Our camper has no dinette. The original floor plan came with a sofa instead of a dinette. While it came with a "portable" table, it was too heavy and awkward to be practical so we came up with a better solution. I made a gate-leg table that can be used in any of three configurations:
With both leaves down, the table is only about 6" wide. It takes up very little space and serves as a nice side table.
With one leaf up, it makes a small desk.
With both leaves up, it is large enough to set for dinner.
As I said, I designed and built this table, but they are available commercially. If interested you can find several choices marketed by Ikea and perhaps other sources.