Hi Gagakev.
Without knowing what the problem you are presently having with the blown air system is, it difficult to say whether the newer Combi systems will or won't suffer from the same issues.
What I do know is a well installed and properly adjusted blown air system can be very effective, Its perhaps a bit more difficult in longer caravans, but as I say correctly adjusted a relatively small temperature differential can be achieved through out the caravan.
As Otherclive has suggested, many caravan manufacturers fits a length of hot air duct under the caravan, If that is not properly insulated that can make a noticeable difference at teh farthest point on the system.
Also air flow is impleaded by every bend in the ducts, so keeping them as straight as possible can make a surprising difference.
In one make of caravan, customers were complaining the end bathroom was not getting warm. We were asked to investigate. We found the caravan manufacturer was using a tee fitting in the duct close to the heater. The hot air entered the head of the Tee, and the straight ahead out put went to a vent, the remainder of the duct to the bathroom was on the leg of the Tee Swapping the vent and the bathroom duct over made a massive difference, directing more air flow to the bathroom.
Also regulating down the output flows through vents closer to the heater improves the flow to the extremities - without losing too much room temperature closer to the heater.
Its all about balancing the system.