DC Cable Sizing Tool - Wire Size Calculator - MM2 & AWG - solar-wind.co.uk
Is saying that you need 00 gauge cable if you want 5% losses for a 300 amp draw (about what a starter can draw) and I would either use a 300 amp fuse or better yet a 100 to 150 amp slow blow fuse that can candle 300+ amps for a few seconds.
If you want to make the connection to your under hood battery lug safer then put it in a piece of radiator hose with zip ties, also make sure everything is very clean and coated in electrical grease or you might melt something.