I want to add a small activated charcoal canister on my gas tank vent. Is it just activated charcoal in the canister? Thinking something very small any thoughts?

The "trick" with an evap charcoal canister system is purge flow during operation.
This dries the charcoal out.
It is just normal activate charcoal, nothing special.
It acts like a sponge that requires drying out during use.
Everything in the world uses a purge valve and engine vacuum to dry the canister except.

The stock T4 914s...

Adding airflow from the cooling system directly into the canister and venting that into the air filter housing is the EASIEST evap system I've seen yet.

It's Genius!

You could vent to the air filter OR you could vent to the atmosphere.
It would only put out vapors during use and as long as you vented those correctly you probably wouldn't ever smell it.

Personally, for a street-based car, I'd vent to an air filter and ingest the high-end hydrocarbons.

When the very first emission controls were added back in 67-68 they got rid of nearly 70% of the emissions with two simple systems. PCV and Evap.
Evap from gas tank was worth 35% of total emissions...

I want to eat my stink!

KISS it...
Just adapt something like a late 914 system into your car.

Ah that makes sense. Not sure I want to get that crazy.

The 914 system is the EASY BUTTON!
Nothing to it.

I once taught "Engine Performance 101" at my local Community College.

Trying to teach something IS the very best way to learn it yourself...

It was the MOST eye opening thing I ever did in college because I got to see what the college wanted from their instructors.

It's a money game, pure and simple!

What I learned (automotive) was the progression of emission control devices, their effect on engine performance, and the resulting changes over the last 50 years...

The when, the why, the changes that came after BIG TIME!

For use on the streets the ONLY reason to NOT use both a PCV and EVAP system is if you have a complete perfect concours example of something that didn't come with it in the first place.

I once told a Bloomington Gold 63 Vette owner that wanted EVAP to build an external garage as adding it to that car was sacrilege in my book. His wife bitched about its odor in their garage...

ALL of my street cars will have active EVAP and PCV. I will use a series of catch cans and filters to not allow the heavy hydrocarbons to hit the intake but the light ones will get burned!

If you also apply modern build techniques and accurate DFI you can make a serious preformance car that is also multiple times cleaner than the original today.

From no emissions and crappy build specs to modern full-on stuff is about 1000/1

Yep, 1000 brand new 911s are cleaner than one early one.
Bunch faster as well...

Charcoal, pelletized form. Pretty cheap stuff online.

you forgot one thing.
it also vents back down the hose to the air bleed off the fan.

yep its simple. what you would call analogue.
uses the charcoal as the valve.
but once it gets past the charcoal its got a straight shot to the atmosphere.
and if you did too many short trips and not enough freeway blasting, the charcoal soon got saturated. even back then when relatively new cars.
everything thinks of these things operating in purge mode, ie engine running.
but they are in fact designed to do their job after hot shutdown. thats when the fume load is coming off the engine but the whole system is not running in terms of consuming vapors.

the systems back in the early 70s were required to be warrantied for 50.000 miles or 5 years. if you read the emissions warranty and original service schedules for the 914s (and US model VWs of that period) there was a major service required of the emissions system and replacement of the cannister at 30,000miles. VW could not in fact make their analogue system work over the required time and miles dictated by the EPA. it is KISS, but was not in fact successful technology? at least in EPA required performance terms.

but don't get me wrong. its still a neat little bit of kit.

i got right into this with research on the 1.8 L jets.
thats when they changed the hook up on the cannisters from the porsche plumbing to the VW plumbing. and i know why. like you say. it only had to deal with fuel evap off the tank and the crankcase after hot shut down. no fumes from carbies (at least when it came to the fours).

but interestingly prior to the L jets the 914s had a hose hook up inherited from the porsche design for 911 engines with carbies.

.....whats that line everyone spouts, a bit unthinkingly that the porsche engineers knew what they were doing? .......not always. sometimes the VW engineers knew what they were doing and it was not the same thing.

its a tricky little thing the VW air cooled evap system.
it relied heavily on making sure you did a bit of steady state freeway or autobahn style running to flood the can with oxygen and complete purging regularly.
otherwise you were pumping those vapors out.
i think what happened is the EPA caught up with porsche on this around about 1973.
they were monitoring all the various manufacturers and their systems with long term testing since the introduction of evap in 1970 and had determined some were not cutting the mustard of making it to 50,000 miles or 5 years. there was a hiccup in there for 914s and 911s that happens around the mid way through the 74 model year. the evap systems could pass the initial new car test but were not making it through the long term duration monitoring.

i shouldn't be interested in this stuff. but aus and japan closely followed our friends across the pacific and adopted the system a few short years after you guys. way in front of europe who remained pollution recidivists for decades until relatively recently.

and you are right. the most remarkable thing about closed crankcase vent systems and evap control systems was they knocked out pretty much 50% of raw hydrocarbon emissions in one foul swoop. with zero effect on engine performance. both are the last things you should ever take off a car.