I used plywood work platforms that were given me by a previous RV-8 builder when I did my -8. With the -3, we tried something different - we filled the bottom of the fuselage between the bulkheads with moving blankets, right up to the level of the bulkhead openings. Add another layer or two on top of those, through the bulkheads,and you will distribute your loads very evenly over the belly skin. It's worked well so far, and the -3 is VERY tiny inside, so I was afraid of damage just due to being so closed in, and elbowing the skin. No damage to date, and much more comfy than hard plywood...
Paul