BIG roasts are why I LOVE summer here in the land of Oz!

Do you, perchance, own a weber? (kettle bbq)
I crank up my weber to the hottest it will go (usally about 30 heat
beads each side)
and when the coals are red hot, plonk a whole rump (smeared liberally
with wholegrain mustard) in, cover the bbq and walk away.
For a whole rump (around 4-5Kg) it usually takes around 3-4 hours.
Seriously, I won't do large roasts by any other means.
The end result is moist, tender, beautifully crusty on the outside -
and fan-bloody-tastic for sandwiches for the tribe for at least 4 days.
Unless we are descended on by the ravening hoardes of
neighbours/friends, who get wind of what's cooking!
One of the main tips though is to allow the meat to stand, after
cooking, well covered in foil and off the heat, for at least 30-40
minutes.

Just my 2¢ worth of advice.

cheers,
LadyJane
--
"Never trust a skinny cook!"