I played the game for a few hours yesterday. I was setting up laser turrets (Mk. I) and fortified barriers, but somehow the slimes got through and destroyed everything in a matter of seconds. I did try to kill them but there were too many
Yeah, MK. 1 Turrets don't exactly do a lot of damage. The main reason your base was probably torn to shreds was because of white slimes which ignore defensive structures and go straight for the main structures. Since there wasn't enough damage output the turrets couldn't stop them and were destroyed; the following collapse leading to a domino effect of your base being destroyed.