It isn't quite obvious as, for the TF300T the 4.2 bootloader is required, but only the latest version of TWRP can install it and it is only compiled for the 4.1 bottloader...
Maybe i'll see with @flumpster
but seeing how many people bricked with the 4.2 BL I'll make a try with the 4.1 one and the latest TWRP recovery available.
Thanks for your answer anyway
- Asus Transformer Prime TF201
- Samsung Galaxy SIII