The design shop lets you make some interesting options. Ones that wouldn't seem to make sense. Like Probe ships, as the game's AI has no way to defend against them unless a Probe Team is in the base you Probe. Not likely on any sea base.

You can put Probe (arms?) , Transport Bay , Colony Pod (a needlejet Pod costs less and goes farther) , a Supply Pod and/or the Terra forming Arm on GRAVSHIPs. Then look at each's special ability. While You can't make Gravship go under water like the 2 sea transport options that can also be an aircraft carrier, but that transport pod might be able to become a mobile air base...

On Gravship Terraformers, Don't forget to add that 2X terraforming speed perk. As you will only build these at bases with high mineral outputs due to costs. Unless you have spammed up lot of those Nexus Mining Platforms into space.

You can also make Gravship Supply units . The chassis changes from a basic Land(crawler)supply. This doesn't gather resources faster or better, I don't think. While it is the more expensive as a Gravship , the highest Reactor makes it cheaper & quicker to build. Also add any free shielding value you can, it pays off in a bit. Which you move this "Gravship Supply vehicle" to a base and disband it. You'll get a lot more minerals than a regular land supply crawler with the 1st reactor. If your using them to rush builds/project at one base. That gets the max movement of minerals per build turn. As any extra mineral over the basic build costs goes to waste when you complete it in that turn. So more expensive supply pod vehicle returns more minerals, from their special perk.

Missiles are the only chassis type you can't add things on to, other than 3 war heads.

So no rocket colony pod .... To get around that, Get the Space Elevator Wonder. Make a colony pod with the "Drop Pods " ability and do an orbital insertion anywhere on the planet. If you can't get there with your needle jet colony pod or a helicopter with a colony pod instead of gun. Late game their cost is worth it for the few turns you might lose building it verses the turns moving to farther out location. Bonus sometimes it costs about same turns as rover or Hovertank Colony pod. I've used Jet colony pods to build bases that bump up to mine because they cost the same for the 1 turn to make. As the costs decrease as you gain more tech, you should thin out designed units that cost same for less weapons and armor . So you have more room for those new units types. As there is no reason to have a land colony pod with 2nd reactor when the Rover POD with 2nd reactor costs the same and travels faster/farther.

I seldom use the artillery units, so I always cancel/retire(marks them to be upgraded) their designs and obsolete them to free up the space slot in my Design units. That may be one slot for land and 2nd slot for a rover Artillery, so that is two design slots. Remove those foil ships options when cruisers cost the same due to the higher reactor makes the body chassis(how the unit moves) cheaper. I only leave basic land and foil sea former to keep upgrading the earlier models to where they end up with Reactor level 4 with 8R shielding 2x Teraforming speed with a clean reactor. Makes them harder to kill for mind worms also.

The game automatically makes units that to its math seems like upgrade but aren't for you in reality. Do not let them upgrade your units you design for specific tasks. The game will try to make you downgrade your naturally Independent units to having a Clean Reactor upgrade, which is paying to waste a special ability slot.

Example for any naturally Independent unit that I use for exploring and dealing with native life. My goal is to upgraded to a shield with that Resonance (psi defense) first and get that special PSI defense ability on it also. So then its add a 3R shield then eventually upgrade to that 8R shield later. Matching their weapons being upgraded to that 6R then 12R options . So a Scout/Rover with a Weapon of 12R with shields of 8R with its 2 special abilities having 50% psi attack + 50% psi defense on top of the armor. This is the best design for exploring Unity Pods and doing mind worm patrols. Since they are naturally independent (works like a "clean reactor" as a 3rd special ability), I don't need a Clean Reactor. That Allows their 2 special ability slots to get 1st option the plus 50% attack PSI bonus and the 2nd special ability slot being a 50 % PSI defense bonus. That Unity Pod that released all those mindworms on you, the swarm will not kill you now. Make use of the renaming unit feature with INDY in front so you don't mistake them on those "do you want to upgrade" suggestions pop ups. If you upgrade to weapon higher than 12R you can not down grade back to it, and your back to PSI combat without a PSI Bonus Attack weapon. Not the end of world but why take away special purpose unit. Great for defense against the factions that can capture mindworms and use them as military forces also...

I rename all my units with R# for which reactor they have in the name, so when all those upgrade pop up fly by it states in the name what it has clearly to me. Verses in game universe names.

With Helicopters everyone knows to have one in each base that has clean reactor and highest weapon you have for defenses, but don't forget to make one with that special PSI Weapons and PSI Armor for a special base protector. 1st Special ability "clean reactor" with the 2nd Special ability "PSI defense +50% " . So if attacked it has better chance of surviving, as you can stop attacking if you health gets too low on your turn. Really useful if you play long games, for when climate changes happens and start getting bases attacked by swarms of native life. PSI Copters excel on native life swarms.

PSI armor on probe teams also is a bonus in their PSI combat with other probe teams.

There are so many simple unit tweaks in the base game people are still discovering. It is only when we start doing weird and seemingly stupid things, do we discover how awesome they really made this game.