Question of the first: I have also installed the PD stand alone converter/smart chargers where the customer wanted to keep their existing panel. It usually fits inside the space opened up when the old converter is removed, a converterectomy if you will......
But most of the more mature trailers on here don't have all that much for either ac or dc distribution. One circuit breaker, a handful of inline fuses and a wire loom just isn't much of a start LOL....
Second Question... No, the PD-4045's converter/smart charger is a circuit board and wouldn't do well standing alone.