[bryanlarsen]

OTOH, most rockets are transported horizontally. (insert picture of Falcon9 going down a road on a flatbed here). This means that they are designed to withstand 1g side loads. SuperHeavy is always roughly vertical. Starship of course has to withstand insane loading horizontally during it's crazy descent and flip stage, but SuperHeavy stays vertical.

[gvb]

The tanks are held in supporting cradles when horizontal so that their weight is distributed properly. Sometimes the tanks must be pressurized when transported horizontally or they would be damaged.