I like to use a piece of PVC on rear mount, and if needed, some as spacers on front mount. It settles in pretty quickly. I've used leather and it is good, but it needs a lot of tightening over time as it compresses into a good seat.
Sometimes moving the rear mount up or down just 1.4 inch can make a diff in vibration, and note also that if it is 4-stroking a lot before it runs in that can make is seem much less smooth.