You don't say which C but they would not fit in mine and I am running one Lithium 12V.
I ran dual 6s for years but we boon-docked and hunted back country with the toy hauler 5th wheel. If you are not doing something like that 2 6 volts is a waste of money even if you can find a spot to place both.
2018 Jayco Greyhawk 29MVP
2019 Jeep Sahara Unlimited
2011 Cyclone 3010 Toy Hauler- Sold
2014 Chevy Silverado Duramax LML -Sold