The capacitor bodies have to be insulated from the case. The easiest way to do that is to use a plastic case. You'll need a 12 position single pole rotary switch to select points along the big inductor. The big inductor can be 40-50 turns of 24awg insulated phone wire on a 35MM plastic film canister. These will then be soldered to the rotary switch.
Re-wrap the long wire around the canister.
You don't need to mount the canister. With all the taps soldered to the rotary switch, it won't be going anywhere. I've built several of these and can tune just about any length of wire to be used from 160 - 10 meters. It's a lot easier than you might think. Provider of quality circuit boards.