If there was a PMA one, don't know. However, you could easily make some seat covers that slip on with the heaters installed. No PMA or anything required, since it is not a permanent part of the aircraft. Wiring should be done with a good quality quick disconnect style like an amp plastic circular connectors, they make inline or bulkhead styles. You can get them from Digi-key. They are one of the more common aviation style connectors. Naturally, you would want either an inline fuse or a circuit breaker. I would put some of the many styles of wire covering to armor them a bit, since the seat moves.
One thing you need to consider, is the amp draw of the heaters. Many smaller aircraft, when you run your avionics, lights and other sundry items don't leave you with a lot of reserve power generation, you may even end up on the - side of the equation. The general rule of thumb is you should not approach 75% of you generation capacity. So not knowing Huskies, I couldn't tell you. You manual may have a power load analysis, or the factory may have one to start you on the right path to customize it to yours. The last thing you need to have happen is to let all the valuable Lucas smoke from your electrical system.
There are loads of seat heater inserts on Amazon, eBay and the like. One thing you will never knows if they make electrical noise on your radios. Aviation radios are way more susceptible, since they are AM vice FM. I also couldn't tell you if they would make such a field that your compass wouldn't swing a bit when they are energized. Experimentation may be your only answer.