Nissan Patrol 4x4 (Africa)

Also with the DC-DC it was able to keep the fridge running and charge the battery at the same time very effectively. Fridge use 4.5A (filled with warm beer ) and battery got charged at 5A so it put back more than what was used......

Ok we have discussed this before ......let me give you the facts and then decide for yourself....
A agm or crank battery needs charge rate of 13.8v so is happy to charge via solenoid very thick wires needed to limit volt drop and can go in engine compartment barely happy with ambient temps of 65 deg they dont want to be discharged below 11v or 10.5 at the most.
Deep cycle batteries and lead crystal needs 14.8v to charge and you can only put 20% of battery size back per hour at ideal charge voltages into a deep cycle.a deep cycle starts beaking down at about 50 deg so does not like under bonnet temps .
then a deep cycle battery life span works on charge and discharge cycles approx 300 on a deltec ...it is calculated at about 50% of battery available voltage so if you keep your fridge in your car and you drive to work there is one cycle gone doesnt matter how many amps you use .
the lead Cristal gives about 3000 cycles and can be stored at 0v for 2 years no problem . you can drain a lead Cristal to 0v without any damage . deep cycle and agm tipe dont like that
agm can start cars and charge much faster than deep cycle and doesnt need the 14,8 v from charging system
so if you want to put battery in your bonnet it must be a agm or a lead cristal

.... so what I read from Tinus is that if you dont use a DC-DC for AGM and LeadCrystal, you will never get much better than around an 80% charge... even worse if the battery is in the back.
DC-DC is way to go, but dont forget a AC-DC as well!

This is the ideal set-up in my view:

Is the one in the link in John's post as good as the C-Tek? It seems to cost a lot less.