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Problem no.1 sounds like a wire has chafed through somewhere and is intermittently shorting to the chassis. I vaguely recall reading somewhere that it often happens on the loom under the car battery, so that might be a good place to start looking.
Does the fuse blow even when all the fed devices that can be turned off are turned off, or does it only fail when specific things are turned on? That might give an indication of where the fault lies. It could be the loom to the hatch lid if it only happens when the rear window or rear wiper is on.
Obviously you ultimately need to find out what's wrong, but when faced with a similar situation with the fog lights on my Mazda (I could find nothing wrong with the wiring) I swapped the fuse for a self-resetting circuit breaker. These trip out when the circuit is overloaded and cut back in after a timed delay. They do allow the circuit to overload, but only for very short periods and so the wiring doesn't get a chance to melt.
Unfortunately, they only go as high as 10 amps, and I doubt wiring two 7.5 amp ones in parallel would have the desired effect. But for the sake of 99p and a bit of soldering (you'd probably need to butcher an old blade fuse and solder the breaker to the pins) it could provide a good stopgap until you get to the bottom of the problem.
Currently in Horatio's garage:
2010 Laguna III Initiale.