Bongo Fury

Looking to re-run 12v cabling from leisure battery to Zig C8 panel on side conversion and fridge (compressor fridge so only 3amps and will have local on/off switch for when not being used). Existing cables look thin to me as need large cables to avoid voltage drop over 4/5m run. Is it best practice to run a earth/0 volt black cable to the back of the van or just use a local chassis earth point. Planning to use 16mm cable so not cheap and doubles the cost to run +12 and 0v cables. Concerned regarding current and good connection without 0v cable as this will be taking reasonable current if running without mains hook up and also carrying charging current back to battery when on site. Can't see this anywhere on Forum. Planning to take feed from leaisure side of split charger so fridge willrun off main battery /alternator when driving.

Personally I always run my own earth, relying on connections that corrode to a chassis and joints between chassis elements can cause some real hard to diagnose problems. Also if you have any radio/tv equipment using these chassis connections then interference problems will be rife as all the other car related devices will be using the same path.