I have westfalia 321 454 300 143 for the main 13pin loom. Auxiliary power kit which puts ignition switched power through to pin 10 of the plug (caravan fridge feed) 300 028 300 113 and finally the fuse box kit 000 055 212A. The fuse box kit needs a relay holder 7e0 937 503e and a couple of screws n 107 214 01. I’m thinking the pin10 power kit is optional.
The relay holder screws onto the edge of the passenger seat base. Have you got a swivel on yours?
Ian