SOldering to the chassis is hard. One thing it takes is patience, you have to hold the gun on there for a l;ong time. Far easier to mount a ground lug and solder to THAT as you suggested.
You could use that sort of resistor, but why start with 2500 ohms? You'd never use more than a tenth of it. Get a 300 ohm resistor or something. Imagine trying to change it ten ohms on the 2500? Now imagine ten ohm adjustment on the 300. 10 ohms is spread out a lot farther on the lower resistance part, a lot easier to get the setting you want.