Just wanted to say that I have just used Rivnuts for the first time - a cunning combination of captive nut and pop rivet.

While they're not strong enough to replace a welded nut, but for lighter applications, What a great invention!!!!
I'm converted! I've been using them into the side wall of tubes, but they would work well on flat panels too.

Cheap too (I got mine off Ebay, along with the tool)

If you've not seen or used them before, have a look.

Whilst I agree they can be a great tool in the car build arsenal I would caution against getting too carried away, they have there place but also have there faults, they can work loose over time, try not to swear when your trying to get a panel off and the rivnut the last bolt is in keeps spinning up! One good tip is to also put some pu adhesive round them before fitting, gives an additional bond and also seals the bare metal edge of the hole it's going on so prevents corrosion over time.
HTH

Try the stainless inserts they are a lot stronger.

I knew there was something other than a normal rivet I should have used last weekend!

I had the same experiences as snakebelly... they work loose and corrode, so when you come to remove said object, you're more stuffed than a stuffed thing lol

Yes, I agree with the points above - I should have said I was using stainless ones into allow box secrion, into which the serations got a decent bite, and the bolts shouldn't need frequent loosening / tightening.

Is that "alloy" box section ? Watch out as stainless and aluminium can cause a galvanic reaction and rot the aluminium to a white powder.

Use steel, serrated rivnuts on steel, much stronger and won't corrode, and countersunk ones beneath panels