earthing is an art in itself, on the more modern military field (post ww2) you need to look at earth return systems (saves money in build and can help protect equipment), rust and the prevention, Radio frequency supression, RF signature (so the enemy can't here you) EMC (compatibility so you power systems dont muck up data) and finally EMP, Electro Mangetic Pulse (A-bomb or pulse weapon)
for catweasle the big LR problem is Alli and steel, you get the electrolytic at contact points (including any dissimilar metals bridges by water) and the alli works as a big sacrficial annode)*** too late again ***
the change from + to - to slow down the chassis rusting.
a good point but off topic some what - if you use those nice shiney stainless steel bit on you rebuild, those original (rare) plain steel bits will corrode like billyoh, even if they are not touching (this is a big problem we have at work big black plain steel sausage with a nice shiny stainless and err very heavy metal steam generation plant.