With the fuselage levelled at 0 degrees I have done the same using the top of the wing as a reference. At the wingtip a piece of timber jammed between the rungs of a ladder holds the wing level. Pic 2 is skewed but the ladder is definitely standing upright on the floor and not teetering to the side. To give the wing the necessary dihedral it is raised 3" at the tip. It was as easy as adding a 2" piece of scrap timber and 4 x 1/4" scraps of plywood to the ladder prop.