In my opinion carts don't hold enough or wick well enough.
The amount this mod will hold is only limited by the length you can live with.
It is squeezable in the middle so it wicks on demand.
Pic of me squeezing a half empty cart bringing liquid to the surface.
With a 510 batt/atty,another squeezable cart and a couple regular carts in the background.
Parts to make it:
A clear small diameter drinking straw.The kind that come in white paper.
A piece of .325" ID X .005" Wall plastic tube from Zeus Peek Sublite Wall Tubing 0AWG .325" ID x .0050" Wall - SmallParts.com
Plasti-dip in the color of your choice. I got mine at US plastics and used black non-aerosol. Plasti-Dip-Aerosol Or Liquid Air Dry Synthetic Rubber Coating - US Plastic Corporation
How to do it:
Cut up a cart until it looks like this. Other pieces also shown.
Epoxy the straw piece in the cut up cart and plug the end with epoxy.
Seal it so it won't leak on the outside where the round straw meets the square hole.
This is the juice reservoir.
Epoxy the outer plastic tube on. Flat toothpicks in the vents help keep glue from blocking them. Try and seal it up so plasti-dip won't leak in later.
White plastic part is roughed up a bit so plasti-dip will get a grip.
Button looking thing from the inside of a cart is used to temporarily seal it for dipping. Broken toothpick to seal that.
This is the airflow tube ready for dipping.
Finished cart after two dips, button removal and some trimming
Much much harder than simply changing filler material but it really really works well. I hope someone tries it.
From plasti-dip website FAQs FAQ Plasti Dip: Protective Rubber Coating Plasti Dip International
Children can chew on it as far as I can tell.
Most epoxies are inert after curing as far as I know also. But I could be wrong.
The amount this mod will hold is only limited by the length you can live with.
It is squeezable in the middle so it wicks on demand.
Pic of me squeezing a half empty cart bringing liquid to the surface.
With a 510 batt/atty,another squeezable cart and a couple regular carts in the background.

Parts to make it:
A clear small diameter drinking straw.The kind that come in white paper.
A piece of .325" ID X .005" Wall plastic tube from Zeus Peek Sublite Wall Tubing 0AWG .325" ID x .0050" Wall - SmallParts.com
Plasti-dip in the color of your choice. I got mine at US plastics and used black non-aerosol. Plasti-Dip-Aerosol Or Liquid Air Dry Synthetic Rubber Coating - US Plastic Corporation
How to do it:
Cut up a cart until it looks like this. Other pieces also shown.

Epoxy the straw piece in the cut up cart and plug the end with epoxy.
Seal it so it won't leak on the outside where the round straw meets the square hole.
This is the juice reservoir.

Epoxy the outer plastic tube on. Flat toothpicks in the vents help keep glue from blocking them. Try and seal it up so plasti-dip won't leak in later.
White plastic part is roughed up a bit so plasti-dip will get a grip.
Button looking thing from the inside of a cart is used to temporarily seal it for dipping. Broken toothpick to seal that.
This is the airflow tube ready for dipping.

Finished cart after two dips, button removal and some trimming

Much much harder than simply changing filler material but it really really works well. I hope someone tries it.
From plasti-dip website FAQs FAQ Plasti Dip: Protective Rubber Coating Plasti Dip International
Children can chew on it as far as I can tell.
Most epoxies are inert after curing as far as I know also. But I could be wrong.