There can be condensation on any van surface that is cold and the surrounding air is warmer. The moisture in the air condenses from invisible vapour to visible water as it's temperature reduces. Usually it's a transitory effect until the air and surface temperatures equalise or get more equal. The effect is increased if you add moisture to the air by having warm people breathing out moisture, boiling a kettle, running hot taps, drying clothing, cooking etc. Constant air changes help in this respect but as that means bringing in cold outside air, it also means plenty of heating is needed.
Eriba Tourings are really no different to any other van in this respect, though the metal roof rim, which borders the poptop is near a constant source of cool exterior air and can have condensation on it.
Eriba Feelings are fairly few and far between but are likely to have a similar rim to their poptop. Eriba Nova's don't have a poptop but like most WWB's will probably have condensation somewhere at some time.
In truth Eribafolk is a bit of a misnomer as there are very few Feeling or Nova owners represented and the vast majority of members join because of the Touring range, so you'll not get too much direct experience feedback on the other models.