I have installed and re installed a small device which automatically switches the charge from one battery to the other when the main engine battery is full. This means I can run the inverter and the interior lights etc off a battery that isn't the engine starter. So no risk of finding myself stuck in a field with a flat battery. I've also wired in some mains sockets and stuck the white LED fairy lights to the ceiling.
I drove her to Watford and back on Sunday and the exhaust stayed on so I'm confident that it's a good solid fix. It seems that the problem with her losing power on hills is related to the fuel leak so I need to have a look at the fuel pump. But with a good exhaust there is a noticeable difference.
I used the large perspex domes from some broken Harmon Kardon speakers and stuffed the red and blue fairy light LEDs in them and they look great. They'll look good on the roof though only when parked up in disco/festival mode.
I'll take some photo's soon.