Early LI batteries had a tendency to FLAME ON due to crappy control systems. 
Newer ones .. Well any battery can do it Even lead acid. but the odds have gone way way down....  I used to sleep atop a Lead Acid and still sleep beside 3 of them..  When they get replaced I'll be going LiFePo4  
I'd go with the current battery location..  If all else fails a good metal smith can easily weld up a battery box for you..  just 5 flat plates some holes and a lid. the lid can be other than metal if you like.  Well painted plywood and 1x2 edges.