I have a second battery in the LR3 that runs all aux systems: fridge, HAM, inside rear ceiling lights, etc. I would not run things off the starting battery even with a solar panel to keep things charged. Use Nat Luna splitter/charger to keep things separate and a solar panel controller (Sun Saver 20L) to monitor the panel and battery charging. Been working well for 4 years. I do not keep the controller under the bonnet as it might be compromised by water intrusion, only hook it in the system when parked while camping. The panel is a foldable model with a longer cord to allow it to be placed in the sun while the LR is in the shade if any is available.
There is plenty of room in the aux battery box for a full size battery.