Hi @IndySkies,
After creating a new volume envelope line, have you double-clicked the place on the line where you wish to add an envelope point(s). You can also 'right-click> Add point'.

FYI, in case you are not aware the Shift+V keyboard shortcut creates a new envelope, whist the 'V' key, shows or hides the exciting envelope. If you wish to drag an envelope point horizontally without changing the amplitude position, hold the Alt key whilst dragging.. or visa-visa, hold the Ctrl key to hold vertical amplitude. The 'Edit> Tools> Envelope' tool makes it easy to work with multiple points at once.
FWIW, I have recently asked the developers to add the 'Vegas Pro' envelope feature... make a selection and dragging the envelope line automatically inserts four interpolation points. I do not know if this is possible or if they want to.