Many years ago I built a 5-band trap dipole as shown in the '68 ARRL Antenna Handbook. I took it out of the closet and uncoiled it, and everything other than a few solder joints looked fine. So I laid it out on the grass, at the very edge of the yard.
Meanwhile a friend with a backhoe came over to spread some gravel... and for some reason he backed up so far that he ran over one trap.
53 feet of wire with the trap at 32 feet, and the tire hit the trap absolutely dead center perfect. I couldn't do that if I were TRYING to. Anyway the Air Dux coil is flat, and the vacuum cap is open to the atmosphere...
So - I looked up the price of a new length of Air Dux 2006 (6 tpi 12 ga, 2.5" diameter). I only need 9 turns (an inch and a half) but they are sold by the ten inch length and I almost had a heart attack when I saw the current prices (well into 3 digits)
It occurred to me that a toroid coil could be used instead of air. The trap is resonant in the 40 meter band. Any reason I shouldn't use one? Power handling limitations maybe? If I go back to the specified doorknob cap instead of the relatively heavy glass vacuum cap, the weight will be about the same.