Col,
I bent up some 20mm square thin walled tube and welded on some mounting brackets. Using existing bolt points, I mounted the frame to the inner guard. To this frame I mounted insertion rubber sheet which I mounted with nutserts so I could remove it easily for repair.
The rubber sheet stops stones hitting the inner guard metal directly. The rubber sheet drops straight down at the back so that stops rocks and stones entering the void behind the wheel where they can bounce off the chassis and into the side panels causing dents.
It is not too difficult to do but a bit fiddly. I did not want to make the assembly too heavy as I suspect over time a heavy assembly could cause stress cracking to the mounting points. I did not drill any holes or alter any panel work to fit my guard protectors. They do make a big difference and I don't have to worry about the noise created by wet road spray or stones causing damage.
For the time being, for the forward section of the guard, I used some self adhesive under bonnet sound deadener which is about 10mm thick. Stones are less likely to hit the forward section but it still happens. When I get time I am going to fabricate a frame to mount some more insertion rubber to the forward section.
I don't intend to fit oversize tyres so fouling should not be an issue. I have made sure that the bent frame cannot come into contact with the tyre at full flex just in case. I have tried to make it so it is strong enough to do the job but not too solid such that it will bend first and not cause panel damage should a branch lodge or be forced up into the wheel well catching the frame.
Depending upon the tyre type and brand, stones being launched into the guard might be less of a problem but with the Continental tyres supplied on my vehicle, stones are a real problem.
Don't forget to protect the bare metal of the bulkhead rear of the front wheels either as this is also prone to damage and will start to rust once the paint is damaged. Insertion rubber will do the job here as well.
Attachment 99942
Attachment 99943