Well, did such about fifteen years ago. We ran two #1 cables forward, tucked into corner formed by frame and underbody. Tried that one cable to frame biz but engine labored when cranking. The two cables made it crank over as normal. The ground went direct to engine block at the mount, the other went to relocated solinoid down near starter.
Biggest problem was rust in the trunk. As the battery charged, the fumes filled the trunk, causing the whole thing to eat away the paint and rust the remainder. Tried leaving the trunk lid open when not in use. Sold the car not long after this, so can't remember much else, other than used some Chevrolet truck mounting to hold in battery.
With lightweight batteries of today, do not see any advantage to this effort. For the cables going forward weighed as much as battery I seem to remember.
ground cable required as steel is not a great conductor- and the little chassis ground straps to the block will likely burn in half, leaving more expensive ground path thru things like rearend/tranny/engine bearings...
and battery box needed to help vapors away- one vent, one inlet, with vent pointing rearward to vacuum a little of the fumes/pull in fresh air to dilute concentration...thats a big problem with hydrogen- hard to contain the smallest known element, as it can basically pass thru just about anything