The first one is a rivet nut (nut rivet?). Mine looks like this, but there are several variants out there.
Some have splines. Use the ones you can get. The one I used is supposed to be attached with a specialized press tool, causing the metal to "cold float". My specialized tool is called "channel lock pliers". I know, it will hardly produce the quality the manufacturer guarantees, but since the screws are attached from the other side, the rivets are pulled into the sheet metal.
I redrilled the deck angle brackets to accomodate these rivets and now I don't need to fiddle with nuts anymore. Nice!
The second solution has to do with removal of the rear deck. Removing twelve square headed bolts to remove the rear deck is hardly tempting - even if you use the rivet nuts above. I have pondered over this issue for a long time and finally came up with a solution I like: Simply reverse the rear bulkhead like this:
There are rivet nuts in locations A and B. The rear deck is attached with a countersunk screw at A and at B there is a longer screw that goes through both decks. Of course, the upper (forward) deck could be drilled at A as well and have a longer bolt go through both there as well.
This works well for my 2010 Tiger, but is likely workable for other vintages as well and I hope someone finds this useful.
Cheers,
/Chris