I always build a frame to keep the bags from going into the spokes. I just slide the frame in the bag and it keeps it stretched out enough to keep from going in. Little angle iron works magic.
Yep, that's what I've done before, reinforce the bags
I had a set of fake leather bags they had a black PVC back but it still needed to be held stiff at the bottom. I used a piece of 1/8' aluminum flat bar attached along the bottom backside on the inside so the bags stayed straight along the bottom
The PVC backing without it was gonna slowly warp and curve and probably eventually hit the spokes over time,
So I reinforced it before it even had a chance to warp
One set of bags was canvas soft sided so I put a 1/8" plywood insert for the backing
The Ply also gave me a place to mount clamps to the rack