Well, I must admit that all my first tries have been a disaster !
Whatever I tried, the PLA didn't stick to the original Rapman bed. The extruded filament was excessively curling and in a few time the all PLA that should have stick to the bed was stuck to the nozzle !
And when I managed to have it to stick, the filament won't extrude anymore after a few time. I think because the nozzle was too close to the bed.

I started to think that I was going to give up using PLA...
But instead I went into some reading about it and how others have done.
I realised that the PLA temps in the default BfB settings are not adapted for me. So I tried extruding my blue PLA (from BfB) at 205°C for the 1st layer (I don't use raft) and then 200°C for all the other layers and it worked like a charm !

I printed this object that is about 8 cm in diameter with nearly zero warping :

Blue PLA logo

Now I can say that working with PLA is a PLeAsure !