Here's the reply I got from Keystone when I inquired about the roof on our 2012 Bullet 281BHS:
Thank you for contacting Keystone RV. Your Bullet does not have a walkable roof. When you need to clean off the roof, we recommend you look for the trusses to step on.
Regards,
Michelle Diaz
Owner Relations
Stay off the roof or use the plywood! It felt spongy for a reason.