in my experience you should use a stopper even before a high build primer. Not much and well worth the effort.
So:
Stopper - and sand
High build primer - and sand
Guidecoat and sand to check for sinkage and low spots
Finally paint
It's well worth getting these steps right if you want a reall firts calss result even with a rattle can of paint
Here's some stopper and its not expensive
http://www.autopaintsbrighton.co.uk/...opper-85-p.asp