Use motherboard, circuits, decor & carved minerals with bits of hull for accent. These can be used to make pretty good looking cyber-recon hulls, visibly covered in the special circuitry that allow them to cloak.
I would like to see stealthough improved, but I do agree with the current standard of ships with invisibility being extremely squishy, physically. So personally I would see creating special stealth-friendly blocks with armor value as potentially OP so you'd see practically minded players just spamming this build.
I think that if there is anywhere to improve stealth it is in giving it the ability to resist forced de-cloaking by underpowered, single-block antenna arrays if enough dedicated reserve power were available and the like rather than adding more new blocks for the express purpose of letting you cast permanent invisibility AND take shots to the head.
I would totally support adding corners, tetras, and heptas to motherboards and circuits. I might even consider a new decorative recon block type that had as little as Zero mass for purposes of stealth/jamming, so long as it had no armor value.