I don't have seat warmers but was a long-distance motorcycle rider for 20 years.
I ran 1500 miles in 24 hours once in temperatures that were in the mid 30s at night to mid 40s in the day.
Along with heated handgrips, all I used was my Aerostich Kanetsu vest.
Keep your core warm and you stay warm. Simple install; put it on, plug it in.
Picture from that day:
It was 14* on the Cherohala this Day: