I have had a Skytag on my 90 for about 4-years now and last weekend installed one on my motorcaravan (to replace the factory installed Tracker which I dislike intensely).
Wiring up is simplicity itself and it comes with instruction but if electrics are not your thing then perhaps there is someone local who could help?
You need a permanent fused supply (5A is more than enough) but you don't have to go looking for one, you can feed directly off the battery via an in-line fuse or aux fusebox. The wires on the unit itself are very small so I recommend soldering any connections.
Most important thing is where to hide it and when that is decided, how to run the wires. I am not going to discus on an open forum the best location but to be perfectly honest there aren't a lot of places anyway so try to be original. I have to say that I am really chuffed with the location I used but bare in mind that the unit needs to communicate so before fixing it into position contact Skytag and make sure they can read the signal. They are really nice people and happy to help, on more than one occasion they have sent me a Google image of the location where the vehicle was parked so I could check signal strength.
One thing I love about the Skytag is the battery disconnect feature.
I SORN my 90 for long periods and last year my 13-year old Bosch battery decided it was time to expire very soon after it had been parked up (can't complain as it had given perfect service up until that point) so when I got the text I checked the vehicle and sure enough the battery had died. Without the Skytag I would not of found out until I went to the vehicle.