Holding the cavegirl suit up high, you try to remember how to put one of these things on.
"It opens at the back." you remember, turning it around to reveal a giant split down the back.
You attempt to fit one of your legs into the suit first, but you just end up clumsily kicking at it while it flops around like an empty sock. You realize that if you keep this up you're going to slip and break your neck, which would possibly be the most embarrassing way to die on a trip to prehistoric times, so instead you decide to start with the head.
You pull the slit at the back of the head apart, examining the tiny silver electrodes lining the inside of the scalp. This is the part you had been dreading. Taking a deep breath and collecting all the bravery you can muster, you pull the hood of the suit over your own head, and immediately feel the sensation of the suit's face bonding with your own. The suit's skin tightens around your skull instantly and then smooths itself over, seeming to thin out until you can't even feel it any more.
"Testing, one two three." you say, "Three plus three is six."
So far, so good, you think, looks like cavegirl brain hasn't taken over.
You slide your your arms into the "sleeves" of the suit next, once again feeling the suit shrink to fit you just as snugly as your own skin. You experimentally flex your left arm, noting that no wrinkles appear in the smooth skin. You give it a pinch and let out a surprised yelp when it hurts just as much as your own skin would. There appears to be no separation whatsoever, as if the suit's skin is now a molecule thick and firmly glued to you. If you remember the Doc's original lecture correctly, that's basically true. It's blended to your own flesh and will even heal from a cut. That's why you need his special gun to remove it.
With the suit now securely attached to your head and arms, you can now more easily step into the legs, bending over slightly and pressing your hand onto the wall of the time machine for support. When you're done, you're left with a pair of smooth legs with plump, muscular thighs, the increased bulk supplied by a complex series of internal structures and "bio-gel", whatever that is. You give your dainty toes an experimental wiggle, and then prepare for the other part that you had been dreading.
The crotch of the suit is fitted with a strange little cup for your penis. As you gently place your manhood into the cup, you feel a rough tug as the crotch of the suit violent pulls itself back and smooths over, and it feels like your dick and balls are pulled back and flattened with it. There's no pain, but the sensation makes your eyes water. Next, the split at the suit's ass closes up as the plump ass-cheeks cling to your own and merge with them, leaving you with a thick girlish butt. Just as you're taking a moment to feel your jiggly new behind, a sudden intrusion causes you to double over in pain. The suit's rectum extends a short length of tubing that merges with the inside of your colon, allowing you to go to the bathroom without having to remove the clonesuit. You cry out in pain as it happens again, somewhere in your crotch this time. You're not even sure what exactly the suit does to your manhood, when when you check between your legs you can only see the flat smoothness of a woman's crotch, broken up by a pair of plump lips. You give it an experimental cup with your right hand, shuddering at the sensitivity of your fake pussy. There's seemingly no room for your manhood in there. Of course your new equipment doesn't come with an actual vaginal channel, it's simply a replica of the outer parts of a woman's anatomy, a remarkably accurate replica as far as you can tell, complete with a urethra that actually allows you to relieve yourself.
With the worst part over, all that's left is to fit the torso area of the suit. The process is quite clean, the split at the suit closes up as if an invisible zipper is being pulled upwards, and the skinsuit shrinks, tightens around your body, and merges. Internal structures painlessly pull your waist inwards, giving you a slight hourglass shape, and as the neck of the suit tightens around your own, the process is complete. Looking down at your seemingly female body, you do what any man would do and cup your average-sized breasts. It's a little bit disturbing when you can actually feel the sensation of your hands groping them.
"Testing again, one two three." you say, in a clear, feminine voice. A device lining the inside of the suit's neck alters the pitch of your voice, "Three plus three is still six." Nice, it seems the inhibitor chip is still definitely working. No cavegirl brain for you. You tap the back of your head appreciatively. "Thanks, little buddy."
All that's left is to put on your outfit. You step into the toga and pull it up past your legs. You hit a hitch when it gets caught on your plump ass, which refuses to squeeze into the toga. You grip the garment tightly and perform an embarrassing hopping motion, which causes your ass and tits to jiggle in an uncomfortable way, but your efforts eventually pay off and you manage to squeeze yourself into it.
You slip your arm into the single "shoulder strap" of the toga and pull it up to your own shoulder. One of your artificial tits is still hanging out, so you tug the toga up with one hand and press down on your tit with the other, until you manage to get it snugly tucked in.
If you had a mirror available, you would see that you now resemble a real cavegirl. Or at least a regular girl in a cavegirl Halloween costume. You're not sure that the pigtails are historically accurate, and you don't look nearly bulky enough to survive in a fight against a sabre-toothed tiger or a triceratops. Wait, did those exist at the same time as cavemen? You never paid much attention in history class.
You remember that's why you're here in the first place.
"Well, here goes nothing. A+, here I come." you say, as you press the button labeled "EXIT" and the door to the port-a-potty swings open.