The RP is basically a bloodtest and an x-ray of the chest.
You have to do a complete new initial medical class 1 either there or in the UK I think. If you have problems from before, I would spend the time and money to get everything sorted out in advance before heading to Doha. Sorting those things out after joining is not a big issue but it takes time and is a source of great frustration since so much is on stake for us careerwise.
Good luck to everyone and enjoy!