1) I think the clutch drive bit would work well, measured the screw and it looks like a 5/32 which is a common size for these type.
2) All those different screws requiring different bits are completely ridiculous, and I could strangle the idiot that thought these clutch style were a good idea; someone sure thought they were being cute.
3) The TT I own stopped production in the mid 80's, so no help there.
4) That screw I took the picture of is as about as good as they get in the trailer, most are rusted and some nearly round (as though someone, not me, has tried removing them with a phillips!). I have never been able to get those screw extractors to work. And that would most certainly crack the plastic.
When I get to a PC with internet I'll post a few more pix of screws in interesting places.
Thanks everyone for helping me out on this. Trying to get the rest of my projects done before selling.
I just ordered 2 clutch driver bits through Grainger. I'd just like to say though the shipping charge was $9.77 through UPS. They didn't have a US mail option, considering they could stick them in a small padded envelope that would cost them maybe .50, $1.50 max to mail and of course you can't forget the $1 handling charge, so that amounts to $3.
Oh, and Manuka...... a Triumph? Really? I think you have a "screw" loose!