I don't know the Redhawk - but my Eagle only had room for one battery - and I got two in it.
First of all, the battery box was taking up a lot of space, I took it out. After measuring carefully I found AGM batteries with dimensions where I could get 2 in the compartment. You'd be suprised how many different sizes of AGM's you can find, mine are taller than they are wide.
I was able to get rid of the battery box, and not worry about venting the batteries because I used AGM's which won't leak and vent so very little gas (only under extreme circumstances) that they aren't a problem.
I ordered the cables and a 2 battery cutoff switch on Amazon.
Don't know if this idea will work for you - but it only takes some careful measurements to figure out.
Buddy Ray - Atlanta
Jayco 2016 Eagle HT 26.5RLS
Ford 2016 F150 Lariat, 3.5L V6 Ecoboost
Max Tow Pkg, 36gal tank
Reese Sidewinder and Reese Titan 16k hitch