Tightening a nut in a tight space
I would propose that you go to a pawn shop or thrift store and get an open end wrench. 

You could then grind away as much of the sides or the shoulders as you can but still leave enough so that it is structurally sound.  ( will not bend ) 

If you do not have a bench grinder then clamp it to a work bench and use an angle grinder. 

OR, try a universal style wrench, 



This kind fits over the nuts and allows you to tighten it in one direction and then rotate it back without having to take it off of the nut. You may need to grind it as well.