i think bass all the way from firewall to wing seat would be fine, just a small wood change during the build, not as much hassle as making a whole 1/8th ply plate. for me that was just easier as it was after i built it.
my landing was light but the grass length proved too much, last time it broke it was almost exactly the same place.
what i saw when it snapped was 6 tiny bits of liteply going in different directions ( formers ) and soft balsa longerons. these trying to stand up to a force of a 5lbs plane trying to stop dead from 10mph 6" away was too much for this area.
Bass would spread the loads into all the liteply and solve the twist problem, a ply plate would be the bulletproof solution for rough fields and unsure landings.

like i said above, i do recognize everyone else harrier lands all day long no problems if they get it right. Cartman can, but long grass and sudden stops don't work.