Interesting, maybe because I'm a tech by trade but I find it to be one of the easiest thing to do and the S10 in general is easy. You should try a GS, not difficult but a pain, those Germans do things differently for sure.
The fit and finish is extremely good on the s10, if you try to make things fit you will struggle and possibly break things. Like most things the trick is NOT make it fit but to make it naturally fall into place without forcefully making it fit, like I said the fit and finish is very good.
Some times looking at the mounting surfaces and getting a mental picture on how it fits together will help over just fighting with the panel. This is especially true with the seat.
The seat hooks in and then the latching has to lineup, if it doesn't it will not lock. Getting down and visually looking for alignment can help. Plus making sure the latch itself is not stiff or in a closed position.
BTW, if your using that awesome allen wrench from under the seat, my advice is spend the coin and go buy a real tool.
Get your self a long handled allen screw driver, it makes a huge difference with the panels.