I've bolted on full length travellers many times but you may need a helper for bolts right in the center of the beam.
Cordless screw driver, ring spanner, packing tape and a stiff batten. (Helper drives electric screw driver for the middle ones.)
Tape the ring spanner to the batten.
Packing tape over washer and down sides of nut.
Nut should just fit into the ring spanner with the packing tape. Not too hard as you have to wiggle the ring spanner off the nut when it is done up.
Stick hole in packing tape so bolt an go through washer.
Put center bolt in first and slide batten in until it hits the bolt. Then carefully move it around until you can feel the bolt go in the hole in the washer and drive the bolt with the electric screw driver. Then do the next one out from the center. Makes it way easier to do it in this order.
Whenever I do a task like this that requires a lot of care and patience I just keep reminding myself that
"This is a game of skill".
Good luck.