It seems clear from your description of a "diy 20a rectifier" and "parts missing" that the system in your caravan has been modified. We cannot know what other features may have been revised away from standard and how that may affect the performance or safety or the remaining equipment.
I do not recall any caravan manufacturer offering an 12Vdc to 230Vac inverter as a standard item. However mst were fitting Power Supply Units, which used 230Vac from the External hook up point to produce a low voltage DC for running lights, and the control circuits of space and water heaters, and fridges. These could run some caravans without a 12V battery but were usually better if a battery was used.
Because of the modifications, you would be better getting a local expert to check it out and make any necessary recommendations.