If the ply is affixed directly to the frame; I'd don some work clothes and safety glasses, grab a long screwdriver, and wriggle around on my back underneath it, poking away with the screwstick to sound out any soft spots.
If it's solid, obviously there's little reason to remove the floor.
Being a Gillig, its unlikely it lived it's prior incarnation where road salt was a concern.
Kudos on the bus!!! When waiting fills, share it's specs in your profile/CP.
And an official welcome to the asylum!