My Bikase Elasto Beetle Phone Bag (https://bikase.com/product/elasto-beetle-phone-bag/) tends to squirm to a side, regardless of how tight I make the securing Velcro bands. I saw on Thingiverse a bag support that fits the formed contours of a modern top tube. My Specialized Hard Rock, however, has a classic design round tube main triangle, so I designed a similarly support that fits the top tube diameter, as well as the width of the bag. The FreeCAD drawing is included if you want to tweak the dimensions to fit your frame and bag.

Top Tube Diameter: 28.79 mm Bag Width: 87.5 mm

Resolution: 0.2 mm

Infill: 15%, Triangles

Raft: No

Brim: Maybe

Supports: No

Filament: PETG, ASA, ABS, Nylon