Ive just fitted Wickes MDF skirting in my conservatory & for the firs time scribed the internal corners rather than cut both at 45 degree (which I did elsewhere in the house). This was miles better & resulte in perfectly aligned corners, whereas before they'd always not meet a
45 degrees & need a squirt of flexible filler up the join (looks OK but corners are then rounded rather than nice & sharp). External mitre are more difficult to line up perfectly in MDF as there is little giv compared to timber. It sounds like a bodge, but I use plastic car bod filler (isopen - the good stuff) up each side of the external corne then a bit of fine sandpaper to sand it into a nice sharp corner. Onc painted, it looks ace-- Pufter