I’m looking to build a rough terrain push type wheelchair. I think a rear caster or a center rear wheel would work best.
My wife and I enjoy going on walks in parks, but it is challenging with a regular wheelchair.
Check out "jogging stroller" on google images.
Now take that design, but place the single wheel in the rear, making it a caster.
Use a bicycle head tube and fork to make that caster, with negative head tube angle.
20 Inch wheels minimum, 26 inch would be even better.
Should roll perfectly anyplace you dare to venture.