Oz,
Various outlets (car radio suppliers) have a product called spiral wrap. MCM sells it in various sizes and it simply just wraps around the wire bundle.
There is obvious diminishing returns with wire sizing. To halve the loss, you need to go to #6 (.00047 or approx. .0005 ohm/ft.) which becomes a problem with weight (more than twice the weight) and drawing the larger diameter through a structural member. In the above example you would drop 0.2 volts instead of 0.4 volts. There are many other losses in the system so the electrical design must minimize those losses within reason. A warm battery will have higher resistance and a cold battery will not be able to make enough chemical reaction to produce full current. (old northern trick in winter is to turn on headlights for 30 seconds to get battery warmed up before asking it to crank at 0 degrees.) Connector resistance adds up (two for each connector) especially if the crimps are bad or the connectors are loose. Each circuit breaker adds a little and the speed controller is not perfect, it represents about four feet of #10 all by itself.
This is an article about batteries in the White Paper section....
http://www.chiefdelphi.com/forums/pa...le&paperid=366