Yes just take up the plywood floor, clean the underneath and its best to cut the matting to shape then roller on the resin mix. It goes hard in a few hours and the smell tends to go after a few days.
Because the fiberglass is on the metal it doesn't crack or brake as all the weight is taken from the metal.
It's best to leave it as it is as the plywood would rot again. I bought a dye with the same company and mixed it into the resin so my van has a blue floor same as the colour of the van. It looks better than the white color of the resin without it.