Paul,the problem with these figures is they are wrong?. The heater will take 8amps at 2kw but the fridge is 125watts and needs approx 0.4amps not 4, similarly 0.2amps for the TV.
Rob says he has changed "three MCB's",I am assume the same one three times? so can we discount the MCB being at fault in this case??.. but many lower amperage 'site' MCB's are tripped on a regular basis and become over sensitive under these conditions.
Some problems I come across in caravans are, MCB's are designed to take an overload for a time and are rated A,B,C,D, accordingly. The most common 'B' takes 1.45 it's rating for some considerable time...go over that even a little and the time reduces dramatically.
Most manufactures use good quality breakers which should work as designed but sometimes they are over sensitive from new...I found the lightest tap with a screwdriver handle tripped one of these instantly. Another problem I found was a bared wire folded over the insulation before connection and resultant poor connection caused the breaker to overheat..this was straight from the factory!!
One more thought, Hamer has had his breaker 'upgraded' to 16amps, personally I am stunned by this as a 10 MCB is there to protect the circuit as designed?. To allow more than that though it without a thorougher investigation as to the suitability is folly indeed...and as from Jan 1st this year..illegal