Overbuild everything. For things that might be fragile-ish like surface mounted electronics, cast the whole thing in resin. As a sibling poster has mentioned, we shoot things out of artillery tubes these days that have way harsher accelerations than 300g.
300g is nuts. Electronics in a shell is one thing, this is a landing craft. In a prior life my designs had to survive 12g aerial drop loads and we had to make things pretty robust.
It also blew my mind that a human being, John Stapp, survived >40g acceleration and 26g deceleration, in a rocket sled. I believe it was the deceleration that hurt him the most.
Gun scopes are minimum 500G rated. Apparently that's the ballpark for recoils(the reaction force from the barrel becoming a rocket engine, and/or the bolt/carrier bottoming out)
