[SwissJetPilot]

Just a quick comment on the hardware. The screws shown here are off my 2-piece belly pan.

The highlighted screw is an M6x20 button-head, of which there are a total of 10. These secure the pan to the the aluminum frame, and there are a couple versions of the same screw available over the counter from Audi or VW. I believe the taller head is N91032702 but I will double check next time I stop by Audi as I have a couple of other items on my spring shopping list.

I replaced mine entire set last year with non-OEM, shorter profile screws which I picked up locally. They went in great, but they were a PITA to get back out. The extra height of the OEM bolts offers more depth for the T30 bit, which gives the bit more surface area and are less prone to slipping out under load.

Since these will be in and out at least once a year when you do an oil change, the taller button head is the way to go.

Be sure to get the one on the right, with the taller button head.
Audi Part No., N-106-444-01 (M6x22)

 

[SwissJetPilot]

Looks like it's going to be a Coupe vs. Roadster, 1-piece vs 2-piece belly pan hardware selection according to LLLParts.
I have the impression there are some minor differences between bolts and screws used for VW vs. Audi too.
Not shown in the diagram, is the 2-piece pan. The rear aluminum section has four additional speed nuts fixed into the aluminum tray and four slightly shorter panel bolts.

 

[SwissJetPilot]

You can jerry-rig a rivnut tool with a bolt, over sized threaded adapter, a washer and two wrenches as shown here. This guy uses all-thread, but a bolt is much easier - Youtube link here.

 

[SwissJetPilot]

You can use a drill bit to drill out the center rivnut flange and then knock out the nut half as you would a rivet. But a chamfer cutter might be a better option since these are often much shorter than a drill bit and easier to control in a tight space.

If the rivnut is spinning, hold the flange with a small pair of vise-grip pliers and screw in a bolt. Then you can hold the bolt with the vise-grips pliers by clamping the bolt in place to the frame and use a Dremel cutter to grind off the flange or use a steel chisel to remove the flange.

The goal is to remove the rivnut and not touch the frame or damage the hole. So I would avoid step-hole cutters as they can easily get away from you and cause more problems than they solve.

 

[SwissJetPilot]

@ benckj - I was playing around with the idea of using aircraft-style access panels for the drain plug and oil filter some years ago. There are aircraft hobby companies that sell premade access panel kits which are large enough to accommodate access both the drain plug and/or filter. One example shown below.

However with the panel(s) off you have an opportunity to inspect the CV boots, suspension and look around for any leaks that might be starting on the engine, transmission or bevel box.

So I decided despite the PITA removing all the bolts, removing the panel was the way to go. Now to make oil changes easier, you really can't beat the Stalhbus valves.

https://www.ttforum.co.uk/threads/oil-pan-oil-filter-housing-drain-valves.237906/post-9142267

 

[SwissJetPilot]

I would guess SSTL will be quite heavy for a panel that size. Personally, I would go with aluminum since it's both lighter and easier to work with IMHO - but you can run the calculations and verify the weight of SSTL vs Alu for a panel that size of equal gauge.

I'm due for an oil change in the next week, so when the Alu panel is off, I can measure how thick it is and let you know.