In my opinion it's just as safe and maybe MORE safe to run it right down the factory wiring channel under the sill plate
The front battery is originally grounded TO THE ENGINE with the largest ground cable, and "jumpered" from either the battery or the engine to the body/ frame with smaller jumpers.
!!YES!! You need a BIG jumper from the engine to the body or else run a separate large gauge ground all the way back to the battery.