I have had this problem with the old floor in the box. Its what to do ? Their are some of the hard wood lamination that are split. Can see the light under the truck.Maybe 1/16" or smaller.
Put a hard wood ply over it ? But how do you seal it ? What about sound deadening ? Waterproofing ?
What to do ? I was reading a post over at Steel Soldier about sound deadening. They were using something called Peal and Stick. This is a rolled roofing material with a alum cover .
Shop Peel & Seal Instant Waterproof Repairs 3-ft W x 33.5-ft L 100-sq ft Aluminum Roll Roofing at Lowes.com
It seals,sticks to wood ( and just about anything it gets near ) works as a good sound deadener. Water proof.
So this is the way I went. Over this will be cork flooring.