The handiest way would be to paint it using Protectakote paint, clean and sand the floor first.
It doesn't bond well to a gloss finish. Make sure you mix in a hardener and you will need a new brush between
coats so just buy a pack of cheap brushes.
As long as you put a mat under anything that could scrape it then it will more than last the life of the van.
The problem with fibreglass is if moisture gets between it and the floor ( and there are many reasons why this
can happen ) then it has nowhere to go and if your floor starts to rot you will have no way of knowing.