This would be useful for next week, when we come to paint our model, as it speeds up the process of blocking in forms.
You can prepare cardboard panels with PVA to make a less absorbent surface to paint on, which allows you to use a cloth to remove paint easier and it gives you a nice warm mid tone to work on, which is useful for acrylic as well as oil painting. If you have any unwanted board/mdf hanging around you can prime these too. If you are priming paper or cardboard it's worth doing both sides so that the surface remains reasonably flat. One coat, diluted to 2 parts of water to one of PVA sealant should be OK. it looks quite patchy but does dry clear.
When using a white canvas many painters like to "wipe" the surface with a mid tone base colour to get a better sense of values they are applying since it is harder to judge how dark to paint if it is surrounded by white. The buff colour of cardboard gives a nice warm ground but you can make your initial background any colour you like.