Dremel sells a bolt on tool holder That i referenced from a different DIYCNC PDF.
Its shown with a older dremel attached but looks to be the same size as the 300. Look like a plastic vertical spine and 2 plastic radial clamps wrap around the dremel, one high and one low that use a bolt and square nut hold unit into place. The entire unit bolts to a flat service with 2 countersunk screws. Looks durable and well made. If it works might be a great quick alternative if the price is right and is still for sale??
(1)#2615294952- Tool holder
(2)#2615294223- Clamp Screw Nut
(2)#2615294205- Clamp Screw
I will have to call them and see if it is still available and how much.