lensrentals.com and borrowlenses.com are great options.
Don't also ignore the option of buying it used. Then after your trip, re-selling it. Could end up being cheaper than renting (renting is not cheap especially with shipping).
I love the Tamron version.
But you're shooting a crop body, right? The 24-70 is not very wide on a crop body. You are currently shooting with the 17-70 -- so that is losing an awful lot on the wide end. You are going from a 26mm equivalent to a 36mm equivalent. That has a huge difference on the field of view.
And 2.8 still isn't great for dark rides. You may want to consider the Sigma 18-35/1.8 if you want to rent just 1 lens for general purpose and for dark rides. Of course, you can also consider the Tamron 17-50/2.8 or the Nikon 17-55/2.8. That 17-24 range is much more meaningful in most cases, than the 50-70 range. (You can always shoot at 50mm and crop a little to get the equivalent of 70.. if you can't magically uncrop wide shots) .