Electrical Gurus Please Check My Calculations

I have been reading everything I can on this and other forums with respect to charging batteries and running a 12 Volt absorption fridge in a caravan from the tow vehicle's alternator.
Would some of the electrical wizards care to comment on my assumptions and calculations please?
Assuming my alternator puts out 13.69 Volts after the engine has been running for 20 minutes or so (measured at the battery terminals) and that there will be say, a 10 metre run to the caravan batteries (in the front boot) and a 15 metre run to the fridge (toward the back of the van)
Firstly the caravan batteries.
Using Tycab Battery Cable ABC119203 13.56 sq mm (approx 6 B&S) which has a resistance of 1.4 ohms/km @20 deg C, if I assume 20 A and 10 metres of cable I will drop 0.28 V and therefore have about 13.41 V at the terminals of the caravan battery.
Secondly the fridge.
Using twin sheath two core flat AWC26503 which is equivalent to 6 mm Auto and which has a resistance of 4.1 ohms/km at 13 A and over 15 metres, I'll drop 0.85V by the time I get to the fridge terminals. So at the fridge terminals there will be 12.84 V

These calculations do not take into account any other resistances such as an Anderson plug, trailer connector or any terminations or relays that might be in the circuit.

Rosscoe