First of all, I don't like seeing a variac in anything that isn't completely shielded and grounded, or enclosed in non-conductor at all times. If some little kid turns that knob when nobody is looking those rails could be running 120V next time you power it up. Somebody touches a rail then and they might as well stick their fingers in an outlet. In fact, the assumption should always be that those rails have potential 120 (or 130) on them with a variac.
Second, your requirement is for about 20 V. You don't need continuously adjustable voltage up to 130. You don't need a transformer that puts out more than 24 V, which is a very common voltage, and considerably safer for this kind of device. The only thing you needed to find out is how many amps you needed and then to buy a 24V transformer to suit.
So why can't you measure the amperage? Put an ammeter in series (NOT parallel) with one of your 7 heating elements. That should be well under 10 amps, so you won't blow your meter's internal fuse. Then multiply that ammeter reading by 7 to get the total amperage needed.
Then buy a 24V (or 23.6V) transformer rated about 25% or more above your total amperage needs. You can feed it with a dimmer or router speed control on the 120V side for some adjustment range. Put a fuse in line with both the input and the output. Then sell the Variac on eBay.