Heikki,
I must say that I don't like the sight of the fenders hanging below the body, but I don't think the skirting will make it look any better. The skirting will always look like something that's been added on. Looking from sideways-on like these photos makes it look like part of the body - but in real life, I think it will look fake.
Here is the back changed to be like the front as you requested.
I don't see how changing your springs will have much effect - they may lower the frame an inch, but not much more. If you stay with springs, you would need a dropped axle, but (a) I don't think you can get them in Finland, (b) there doesn't seem to be space between the frame and wheel and (c) fitting in the damper would be very difficult. So that's not good, eh?
To lower the trailer, a new torsion axle would be the easiest. Would you need to resubmit the trailer for approval?
Andrew