Finished.
Vehicle mode; front view

Rear view

Robot mode; rear view - here you can best see the engine-style detail on the back of his head. I was inspired by a 4WD Beetle I saw in town...

Robot mode front view

Hardshell reveals his true allegiance! I used a Reprolabel rubsign, but painted black over the edges so it didn't stand out so much.

HARDSHELL - DECEPTICON
FUNCTION: Espionage, saboteur
“Fear not the army of foes you can see; fear the one foe you cannot.”
Profile: Hardshell is the ghost in the machine. If something goes wrong, odds are he’s behind it, but he’ll be long gone before you realise. Cool and efficient, he slips in, gets the job done and gets out.
Self-assured, self-reliant, self-important and self-centred, Hardshell is supremely confident in his abilities, but far less so in those of his associates. He much prefers to work alone, so that he doesn’t have “rooks” getting in the way of his doing the job properly.
Off-duty, however, he loves to spend time in the company of his comrades, mostly so he can regale them with his latest success stories and rub in how much better he is than they are. He has a dark wit and a sharp tongue; he loves to laugh at the suffering of others, and if he’s caused it, so much the better. The only Decepticons safe from his insults are Ravage (whose abilities and professionalism he quietly respects as being on a par with his own) and Megatron himself (who he knows well enough not to cross).
Weapons and Abilities: Subject has below-average strength, but well above-average agility and durability. Personal force-field can be tuned to absorb or bend electromagnetic radiation including light, microwaves and radio waves, making him virtually invisible to most detection methods, as well as allowing him to weather barrages of laser fire with hardly a scorch mark. Banks of sensitive scanners allow him to constantly monitor terrain and enemy activity. Equipped with a series of long-ranged passive scanners, and shorter-ranged active sets. Hands are equipped with an array of cutting torches and welders which he uses in his sabotage work; the settings on these can also be altered to double as short-ranged blasters.
Weaknesses: Although highly durable, Subject’s low strength and lack of dedicated weapons systems means he does not fare well in direct combat. He is often overly dismissive of others’ abilities, allowing him to be caught off guard when an opponent (or disgruntled ally) proves to be more capable than he gave them credit for. His attitude makes him a lot of enemies, including on his own side.
Strength: 3
Intelligence: 9
Speed: 5
Endurance: 8
Rank: 6
Courage: 7
Firepower: 2
Skill: 9