2018 Frame ground upgrade

[mysery1]

I'm trying to figure out the best way to upgrade/replace the small ground (8 gauge wire maybe) wire from the battery to the frame. I want to change it to 4 gauge wire because I'm installing a 50 amp DC2DC charger in my travel trailer. I want to use the frame as the return (negative) instead of buying another 20' 4 gauge cable.  It needs to run through the current sensor which shouldn't be a problem. My problem is the limited space around the negative post. 

[mysery1]

Quit over thinking this and took a 4 gauge cable and crimped 2 lugs on the cable for #10 bolts. Drilled out the lugs with a 15/64 drill to fit the metric bolts for the battery clamp and where the cable mounts to the frame. Ran the cable through the current sensor, attached both ends and called it a day.