(PB is having serious issues tonigt, I will remove the image once they have served their purpose)
I highly recomend manual focus for this stuff. From my experiance auto focus just can't find anything in the dark (wether it's bad auto focuses I have or what I don't know). My eyes are not great either, but they work thankfully.
For focusing you need contrast at the point of the subject at hand, correct? With this image the best spot I can think of is shown by the two arrows, the blue for the most consentrated aria of light in the aria of the subject and the red for the darkest spot in the same aria. That spot where the arrows point to would prolly be your best bet for getting it focused. However this will not be an easy focus it will take some time to get it spot on, don't be afraid to spend a few minutes focusing the image, it pays off in the end.
Now it's rather clear that the point I am suggesting is above the center point of the composition you have, This is easy enough to get around. If I have to correct idea about your tripod it sounds like there is a srtaight up and down extention, is this correct?
If so all you really need to do is raise the camera up and focus then bring it straight down once it is focused, I have done this several times with great results.
also, just because....
A tighter aprature (I.E. 11, 16 or 22) will give you some room to miss the focus a little bit at the price of either exposure time and/or ISO speed, but it's not a clean all.