When I was riveting the bottom wing skin on my RV8, I placed the wing in two position.
To rivet the inner skin, I layed the wing flat like in the picture and all the inner rivet holes could be easily reached while the wing was in the lay-flat position.
I needed the wing to be in the up right position to rivet the outter skin.
However, I did not rivet the rear spar first. I incrementally rivet from the inboard lower spar and progressively moved outboard. I am 5'6" tall and my arm could reach all the rivets using this method. See the picture below. These are the general direction I was using
Also, I dry-run using clecos to incrementally close the bottom wing skin and wrote on the wingskin the sequence that worked. So that I didn't forget the sequence when doing the actual riveting. The 2nd picture shows the scribbling of the riveting step during the dry-run. I saw at least one Youtube video where the builder got trapped in to a corner. So I thought doing the dry-run was important enough for me to do.