The Wiring is usually buried in the caravan wall and is not acceptable.
If the Problem is with the front side light and Tail light then.... The problem could be either Bad connection on the Plug and Socket (Car to Caravan) the Side lights are wired separately (left and right). On a Seven Pin Plug it is Pin 5-Brown Wire for the Right hand Tail and Pin 7-Black Wire for the Left hand tail light. On a 13 Pin Plug it is Pin 5-Brown Wire for Right hand Tail and Pin 7-Black Wire for the Left hand Tail light.
If the Problem is just the Tail light and the front side light is OK then..... Check the wiring in the 'Light Cluster', it is possible to get a corroded connection in there, can you re-make off the connection to be on the safe side.
The other possibility is, 'Somewhere' there will be a connection block were the 'Multicore Cable' from the Plug is split to go to the various places on the van, there could be a bad connection there.
All of the problems I have had over the years with caravans (and Cars) rear lights has been in the Rear light clusters, so I would start with there.
As Roy (Dickers) would say, Long distance fault finding is not easy, I hope this helps a bit.
Elnagh Clipper 90.......... Real Names Mike & Hazel