When wiring for electronics in a jon boat can you use the boat as a common ground like you use the chassis in a car?  Say the tm was up front and the battery was in the back, it'd be easier to run only the positive wire and just connect the negative of each to the boat.  I can't see why it wouldn't work, but I'd rather ask than go through the trouble of doing it wrong:)

In a car your battery is grounded to the cars frame in a boat it is not, so the answer is no

I'm not a fan of chassis grounds in cars....

In the race cars, we always ground everything to the battery. Just me....

Do not do it. It can cause the aluminum to erode away.

Using the hull as a ground is a safety hazzard.  If a positive wire rubs against the hull (which is common) and the insulation is cut the wire will short out.  A short to ground can cause sparks and fire which is something that you don't want when you are on the water.  I would not do it.