Pro-Line made a nice interior for short course bodies. It's been discontinued for a while, but I found some new-old stock at this small online hobby shop:
Bolink used to make one. it was 1/10 TC size, not sure how well it would look in a short course truck.
i want to say Parma made one as well. probably more based on 1/10 on road as well.
i know the Bolink one pops up on ebay every now and then. not always cheap tough.
Are you mainly looking for driver figures? Maybe look at Arrma's Mojave, or Axial Yeti SCORE Trophy Truck.
I don't know how hard you plan to run a SCT, but bodies are going to see a lot of abuse. Attaching an interior piece to a body is going to see that same abuse.