Probably would have been a better idea to get the 2.9t version then, that is not to say you wouldn't still be overweight, especially if it is a 2 man setup, but you wouldn't be so far overweight!. The guy i mention (and i think this was a solo operator) said he carried quite a bit of other stuff too, but going by his weighbridge reading, even with just the tank and water, you would be overweight with the 2.7t.
It is up to you and I'm not your mum, but i wouldn't do it, to much possible risks. And i don't just mean the possibility of being pulled over and having your weight checked. I also mean, if you are involved in an accident, especially if there is question over who is at fault and investigation reveals you are well overweight not only would you probably face a very hefty fine, you may even end up losing your license.