Bailey Vigo fridge not working while on 12 volts

[Revveroo]

I have a 2013 Unicorn Vigo mark 2 with a dometic fridge RMD 8551which fails to chill while on a journey.
Originally towing with 2013 Honda CR-V then changed to a 59 Discovery 4 upon which fridge works! Methinks ah solved problem but now it's warmer fridge warms up on a 4 hour journey and freezer melts!
Had Dometic out under guarantee did not find anything wrong so charged me £ 50!
Dealer had checked it with car connected and fridge works while car stationary!
Is this fridge with separate freezer needing too much power?
I have read related articles regarding needing stronger relays and wiring etc but think Discovery should cope!

 

[Dustydog]

So the two dealers say both car and caravan working correctly.
A real possibility is the earth return not working correctly.Trace ALL earth wires and connections on both car and caravan .High resistances can build up eve though the connection looks okay.

 

[Revveroo]

Thanks! I,m no electrician but car going in soon so,will get that checked plus caravan! Will keep u posted!

 

[ProfJohnL]

Do you have fridge vent covers for the caravan? Are they fitted when you tow?

 

[Revveroo]

No covers and no! Thanks anyway.