Okay - more updates:
The tuckable prototype finally gave up the ghost- after being reformed from a Glock to an XD back to a Glock - I discovered the cracking where the holster body and the belt attachment join was irrepairable. I probably could've coated everything with a few coats of epoxy - but what would be the point? It would've failed at some point.
The next tucker style holster will be made of thicker material. The 0.03" difference in thickness won't mean crap for concealment, but it means loads in the strength of the plastic.
The tucker body is not completely gone though! The body, sans belt attachment - has been reformed yet again - and made into the prototype for the Chest Packer design - this time for my Kel-Tec P40.
Pix of the very early stage prototype Chest Packer:



As you can see in the top two photos, when worn for left hand draw configuration, the gun butt sticks out and doesn't hug tight to the body. This is because the attachment point is between the gun and the wearer's body. When reversed, the gun hugs in a LOT closer, although the draw
could get hung up in the straps.
This is an early prototype, which proved that my basic idea is sound - BUT with some minor changes.
First off - I didn't have a full sheet of kydex to work with, I had a couple old holster bodies - from failed designs, and the broken tucker. The broken tucker had the best, most usable material for prototype 1 of this holster style.
When my order of sheet kydex comes in, some changes I plan on making:
full-length sweat-guard on both sides of the slide, drilled for ambidextrous neck-lanyard attachment. The body itself will be wider, and there will probably be two body straps, or one 2" strap to help pull the holster body in close and provide a stable platform for drawing and reholstering.
The neck lanyard will also have a quick-release buckle with length adjustment, instead of a fixed length strap with no break-away device. And they call it a prototype for a reason, right?

Another thing I'm going to look into is a retention device - thumb break or strap - so I don't have to mould the kydex so tight to retain the gun. I don't exactly feel super comfortable with the gun being able to be jarred out of the holster in this position, even the DAO kel-tec that has the hammer at rest at all times with it's heavy trigger. Murphy is an ass - no reason to make life easier
for him.
So slightly less tension on the molding with the addition of a thumb-break or other retention strap would be good.
My original intent for this type of design would be for casual concealed carry while enjoying the outdoors - hiking/fishing/camping/bird watching - where openly carrying a firearm might draw unneeded/wanted attention from idiots who would call the police on a MWAG type call. It's rare, but it happens. In this scenario, the user would wear this setup under a lightweight button-up shirt. You could throw your fishing chest pack or vest over it to hide the buldge, or a camera case, etc - OR for open/concealed carry while outdoors and your method of dress does not include a belt and belt-holster combo. Some people do like wearing shorts without belts in the woods. I do, occasionally. It would be nice not to have to choose comfort of beltless pants VS having a firearm at hand. This would be for people that don't want to walk around with the fanny pack or a backpack or shoulder holster.
Personally I was planning to wear this rig under a chest-pack while fishing light - that is fishing without toting around my full daypack full of gear. I could conceal the firearm under the pack, and if it's needed, I can always just reach between my body and the chest pack and draw the gun. It might also come in handy for a hunter who wants to carry a sidearm while hunting, without toting a gun around on a belt all day - or someone who's carrying a backpack that would inhibit use of a belt holster. Lots of uses.
I will post pix and more details when I get the 2nd revision built.
Another note:
Pepper is field testing some other items for me now - a magazine carrier for his 1911 (though he doesn't carry that gun much anymore, the wanker) - a very early prototype flashlight carrier, the the IWB Mk. 1 holster that was made on the first page of this tutorial. He got that holster to keep when he traded the Sig back to me for one of my G19's. His first impression of that holster was positive - I'll have him say a few words about it at his leisure.
more updates to come.