I have had this concern myself with locking the keys in my trunk, because I always remove my key everywhere I go and put it in the key holder that was provided with the key, which I attached to my jacket zipper for convienence. Many times especially when its hot out I put my jacket in the trunk when I go shopping, stop at convenience stores or whatever. If I forget the key that wouldn't be a good thing.
I like some of the ideas that some of you have posted here, but my other concern is what if I just happen to lose my key some place and never find it? I wanted a way to carry my spare key on the spyder where I can access it when I need it. I searched around and found these key lockers made by Bell which I purchased at Advanced Auto Parts. They come with a magnetic back which can be held on any metal surface. This seems to work well for me. Here are some pictures to show what I have done.
Key lockers came in a package of two for about $3.00 at Advanced Auto Parts. I did have to file and sand down some of the molding on the handle of the spare key so it would fit in the case, because the key was a little too large to fit. These have a flip top lid that hold the key secure and in place.
The key locker also has a pin molded in place on the bottom edge where you can add a cable, key chain, ect. I added a zip tie for now, but plan to add a spring or a cable to attach it too the spyder.
I stuck the key locker on the back edge of the oil tank which gives it a convenient location to have access to it, yet is still somewhat hidden under the pined panel. I attached the zip tie through the hole that is on the end of the oil tank. As I stated, I plan to replace the zip tie and maybe add a spring or cable here instead. This will keep the key locker from falling if you happen to drop it when taking it off the oil tank or should it fall off for some reason. Although, the magnetic holder really works well and seems to be very secure on the oil tank.
When you need to have access to the spare key, there is no need to remove the panel. Just reach under, pull the key locker out and remove the key.