Mike;
“I have constructed some of the handles using the foam core and fiberglass/graphite cloth. So, you are using the graphite cloth and making your own tubes?”

That is exactly what I am doing, and what I suggest you do for best results.

Yes you can purchase pre-made graphite tubing that the epoxy will stick to under construction. But I do not believe it will hold up under use.
I would not suggest any setup that replied on only epoxy to hold it in place. While I’ve built the offset handles for years, I did not build the “Hot handle design” until using cloth to make my own by sandwiching the blank between the two layer of cloth.


Roger;
The hand warmers are not in the blank.
The warmers are kept in the handle so I can fish with no glove or thin glove on the holding hand and can feel the bites better, wearing a thicker glove on the cranking hand.

It may get a lot colder were you are, but down here (NC) seldom fish in anything below 18 degrees Fahrenheit. I don’t notice it being the back of the hands getting cold, but fingers and finger tips.
While I think the mitten idea is interesting. When bass fishing and making several hundred or more casts a day I’m not sure how practical it would be.

While I haven't tried it yet myself, some people tuck hand warmers inside the cuffs of their sleeves to warm the blood circulating to their hands.

Doing this is supposed to keep your whole hand warm, and if it works, you wouldn't need hand warmers in the handles and can install arbors in them eliminating the need to battle the adhesion issue with these tubes.

Good luck.

Dan

P.S. Depending on the hand warmers, it's generally best to NOT place them directly against bare skin to avoid burns.

We have used the tubing that Lamiglas makes for about four years now. We use Hardwood turned down for arbors. We scuff the inside with scotchbrite pads then use rod bond. Have not had any come loose yet. Perhaps you could scuff the inside of the tubing and then the blank where the rod bond would be applied. Clamp the blank on the ends with some small clamps or clothespins and let set 24 hours. This should give you the desired effect. To my undrstanding there is Texalium, Telexuim, and graphite tubing. We have used all with the same results. It doesn't take much of the rod bond to get a good hold, so it should look very professional. Hope this helps.

Here is a thought, why not compromise? You only need access to the hand warmer at the reel, so if you are building a full length handle, why not go to a 2 arbor design? You could put an arbor at the butt and one half way up and leave the front open for inserting your hand warmer. This way you can have some of the blank-tube connection supported, and still have an opening for a hand warmer. Of course, if you can't get a good bond between the blank and tube, it's probably a moot point.

Joe