As above it can take the weight but you wont go anywhere too fast and give yourself braking distance...
I've had 12 2*2 slabs in the back a past xantia and reckon'd on 30kg each maybe more and she coped, suspension just took a few seconds longer to get up as i had put her in low to help with loading.
Also use some old carpet to cover all plastic and other bits you dont want scracthed or dirty and use one to hang over the rear bumper and the boot lip plastic as it saves scratches on that as well, put the carpet(softest side) facing onto the bumper/plastic bits as it has a bit more give than the hard backing materials
