Highly recommend you use some undercoat.
When you use undercoat it seals the timber and you will use less topcoat, you will also get a more uniform finish.
If you use water based "Solver Maxi PSU" used a 100mm foam roller, and sand between coats, 2-3 coats should do it.
The good thing about this undercoat is, its water based and you can just wrap your roller up in a wet rag overnight while your waiting for the coat to dry, also its easy to cleanup.
1 litre of undercoat will easily do a whole machine, with some left over.