Due to my budget rim purchase with outlandish offset (15X8 +0), I'm in need of fitting some flares (2" poke is legal right?). However this is going to look rather craptacular the moment I bolt my track wheels back on the car and they a sunken so far into the guards they look like hermit crabs.
 
My idea is to make two sets of inter-changeable flares. One set is essentially a moulded copy of the factory guard flare (which will look like a bolt on flare kit) to suit the 15X7 +35 track rims, the other set will be the oversized, moulded to fit 2" extra poke of fat 15X8 +0 wheels. The plan is to trim back the guard to leave a 20-25mm mounting surface along the curvature of the arch, then use a Rivnut / Nutsert / JBWelded Nut? as a fixture point for the flares.
 
I'm looking for some wisdom / advise with using a Rivnut / Nutsert type product in panels like guards, to gauge if they will work for this idea or if they will just strip out or tear out of the panel after a while? Who's used hem for similar things and what's your take on it all?

Dumb question. Could you just buy new track rims and permanently attach the flares? 20mm spacer? :)

Rivnuts are the greatest thing since sliced and pre-buttered bread.  Once you start using them, you'll be looking for a good excuse to put a rivnut into anything that moves and shouldn't.
 
The inserts come in alloy and stainless flavour, and as long as you take the time to make sure the fastener is started properly (i.e. DON'T cross thread it!!)  and don't get your pet gorilla to swing on a breaker bar when you tighten them, you won't have a problem with longevity.
 
A word of advice - don't be tempted to buy a cheap insert tool, get something worthwhile.  Let me know if I can help make up your mind anymore . . .

Have you used the inserts on thin materials? Just wondering if they will grab and hold well on the guards or if I should look towards getting nuts welded or bonded to the materials.
 
Point me to a worthwhile insert tool please.

I've used them in my engine bay where there is only one layer to hold catch can and coolant overflow without a problem.

Hi Nitrous,
One place to look is www.avdel-global.com They show pneumatic setting tools. Don't know if they do manual type.
 
My experience with riv-nuts in another industry, is that the holes for the riv-nuts need to be very clean & tight to the insert to provide maximum strength & resistance to spinning.

Panels - I've used them on in place of the plastic insert that holds the rear mudflap on.  The insert can be purchased in a range of "compression" thicknesses.  You get the one that will suit the material you're working with, including plastic/f'glass - for this you can have an insert that is "ribbed for your pleasure", and actually bites into the material as it is compressed.
 
There are a few tricks to using them.  Don't be tempted to over-compress them, they're not pop rivets!  All you'll do is weaken the thread inside, or rip it out completely.  If this happens it can be a bit of a mission to drill out the damaged insert and start again.
 
Another hint is to use a drill slightly undersize, and finish the hole off with a deburring tool.  As Peter pointed out a clean tight hole gives the best results.  (Try saying that out loud without laughing) 
 
And something that seems obvious, but I have seen it happen.  Check the depth you have behind the insert, and compare it to the length of fastener you propose to use.

I have used various brands and tools over the years and personally love them, however on thin material where you will be undoing and doing up all the time i think you will run into alot of spinning issues unless welded.
 
http://classicdatsun.com/new/ZG-flares_inst.html