Hey man,
On W124s operating the trunk lock opens all other doors and vice verse. So if you power the trunk loch (Same as operating the lock with a key) via a regular FM receiver (Remote) you should be able to remotely unlock and lock the car, a lot simpler than removing the seat and screwing around with vac units. Granted you have done it and that's great, but if you ever need to do it again this is an easier way.
Happy holidays