I would rip up the ply floor, and leave the sides in.
You need to key the floor (sand it down and make it rough) seal edges where ply would meet floor. get some masking tape, tape how high up you want to go, I did to wheel arches and 2 inches above, said why already. get paint brush paint upto masking tape and about inch or 2 down, get roller dip straight into pain tub so fully loaded and roller sides down firstthen start at front of van nearest drivers seat and work to back of van, if you like flying close doors when you do this (warning will give you a head ache) normal person open all doors (this stuff sticks big time. first cost in your van size less than half a tin. then just wait to dry maybe upto 24 hours in this weather then second coat it, more attention and thicker paint nearer to back of van as this is where the wear (I love english grammer, Ewan
) will happen if side doors this area directly infront also.
did I say wear gloves before make sure you do as it is a milk producing animal to get off.
Ian
p.s remember to have fun doing this, I love getting new vans