By the way, caravans are not covered by the the EU Directive. Motor homes are. Therefore, although caravan manufacturers nowadays usually specify a MIRO, there is no common understanding what the MIRO of a caravan does or does not include. Some include what they call 'essential habitation equipment', others do not. On the other hand, for cars and motor homes, the definition of MIRO is very specific.
However, there is can still be a difference between MIRO and kerbweight. MIRO is an ex-works weight. Kerbweight is actual, i.e. after installation of permanently fitted accessories, such as the towbar. Towbars and all their associated parts (fasteners, additional reinforcements, wiring harness, etc.) alone can weight up to about 40kg.
The only weight that never changes is GVW, MTPLM or MAM (maximum allowable mass). There are very slight differences of defintion between the three but they are not worth going into detail here.