I roast mine very slowly,gas 4 for about 2 hrs(covered in foil),then let it cool.I make a stock from all the stuff that has collected in the dish,add a pork stock cube,then slice the gammon,removing any fatty bits.Sometimes I roast the skin separately,high gas mk7 for half an hour to make 'gammon scratchings'
Then put the sliced gammon and the stock in the roasting tray,cover with foil and cook for another hour,gas 5.
The best thing I found with this is the leftovers can just stay in the tin,then be re heated the same way the next day.
Enjoy