preperation is key, make sure the surface is clean and dry and that you also rubbed it down with sandpaper to 'rough' it up a bit, this helps with paint grip the surface. I found using a big paint brush best as my floor has little ridges along it so the roller never worked as good, keep stirring the paint so the small particles keep moving and the paint doesnt clog up, once your first coat is down give it a few hours and then apply the second coat, it will take a few days to dry to the point where you can put your equipment back in the van though.
Make sure you have plenty of ventialtion and also keep it off your hands as it does take ages to get it off, i tried everything to get it off and nothing worked except giving it time. oh and dont buy to much, i bought a 4 litre and a 1 litre for my LWB transit, i only used the 4 ltr so i spent 20 to much