I've seen batteries bigger than the cover in the floorboard installed by fabricating a new battery box that unbolts from under the floor. It's a little inconvenient for battery changes but the floor access panel can still be used for checking the water and cleaning terminals if the battery isn't a sealed top unit.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!