Er... A forward armor bulkhead of invulnerable dockers and rails anyone? Only a few thousand entities... I prefer spawning 'invulnerable'
ghost rails when a rail or docker gets destroyed, that keep the entities in place but renders then inert.
Let me clarify: The core is "Invulnerable" In that it can't be destroyed by weapons fire. It still takes damage, still applies that damage to it's entity's systems, etc.
You can CURRENTLY make your "invulnerable bulkhead" by lining up a bunch of rails, dockers, and cores, and giving them each 101% extra systems HP in relation to the core block you leave as the "leading edge".
I'm just proposing fixing rail dedock by never allowing active rails or dockers to drop below 1 block hp, while directly passing any damage they take to the SHP pool.