I'm after a switch to isolate the leisure electrics when the bus is parked up, not really after a full blown power management unit, basically I'm too tight
I put a switch into the feed from the leisure battery to the leisure fuse box. I also have switches on the feeds from that fuse box into the 12v stuff like fridge, water tap etc. I can turn specific stuff off or with the master switch turn everything off. I got the switches from Maplins.
I have also, used a switch like you have on your wall at home to isolate the appliances like your cooker, couple of quid from Wilkos, looks ok. no expense spared.
This probably Falls under your"fully blown" description, but it's a great bit of kit. www.batterybrain.co.uk
Just make sure you've nothing running when you switch off or on...those switch contacts are only rated for ac not dc so will have a tendency to arc when operated under load and in time burn out.