For convection cooking, I was under the general impression that little venting if any is really expected. The purpose of the fan for convection baking is to circulate the hot air in the oven, not to pull it out (so more air comes in and needs to be heated). Similarly, for microwaving, the fan is used not so much to ventilate the oven cavity as to cool the magnetron (and other parts of the microwave oven circuitry).
A convection microwave often is also a range hood, and for that function venting inside or outside can make a very noticeable difference in how much moisture accumulates in the RV.