removable trans tunnel

Sorry...but you're wrong.
I've worked in the automotive industry for over 35 years and have personally had many issues with FACTORY installed Riv-nuts/Nutserts as have many co-workers.
If the factory can't pick the right ones or install them properly, what chance do we have!?!?

I expect the larger versions for thicker materials would be much less likely to have problems, but the ones holding factory roof racks on various cars and certain sections of flares on Jeeps were giving us issues when new.
Try to remove a rack to paint a roof...spinning riv-nut...every friggin' time there would be one or two.

TODAY made me smile.
A couple of days ago I pulled the box from a 2007-8 GMC pickup. The front right box bolt was apparently siezed and the nut broke off the plate inside the box rail.
Had to cut the head off the bolt to remove the box.
I ended up on a different job and a co-worker put the box side on the pickup bed.
Turns out the nut didn't break clear of the internal plate.

You guessed it.
GM used RIV-NUTS into the box rail to hold the bed to the frame and this one spun inside the rail.
He tried for an hour and a half to tack the riv-nut to the box rail and then use the washer/nut trick to spin out the old bolt but no dice. Tomorrow he's gonna open up the rail and replace the riv-nut with a plate and welded on nut.

It's just the way stuff goes sometimes...Riv-nuts have their place and work reasonably well but they are not 100% reliable.

 

I might be wrong, but being wrong is very good for me.

I have used hundreds of rivnuts over the years on many projects and have not had any of the failures you speak of.

I'll keep using them and proving that the quality is only as good as the installer.

And I don't put much faith in the "factory" either.

 

Yes. Proper installation and torque. Most people are a little heavy-handed. Kind of like this:

 

While you are undecided about what fastener system use, just pop rivet the removable sections for now.
If they need to come off just drill the pop rivets out.
They only require a 1/8" hole so what ever else you choose in the future will be a hole size greater than 1/8" any ways.

Personally, I'd advise you to invest in one of those insert guns as they come in handy when you least expect it and once you have one in your tool kit it will get work.