[lunarhighway]

I don't remember exactly how thick the aluminum is but it's less than 1mm i think. you can easily bend it by hand and you can punch is with a woodscrew after a light tab with a hammer wich is easyer than drilling... this creates a "volcano" shape in stead of a neat hole but considering the thickness of the material this might actually strenghten the hole and prevent it from ripping trough . some nuts and bolts wich washers seem to do their job exelent in holding things together.
Another advantage is you can cut it with metal sheers with little effort and bend it to a tight angle over a table edge or a straight piece of metal.
When folding all edges up 90 degrees creating a 1-2 cm lip the whole thing becomes much more rigid than you'd think... it will than only be able to flex along a few lines, so a few well chosen attachement points and perhaps a little brace here and there will transform a floppy sheet into a very rigid construction.

aluminum twise as thick would seem a better choice but it would cost twise as much and you'd need specialised tools like a brake, to work it.
after quite some months on the road the tray still looks in top shape... and it keeps the engine much cleaner too.

i'm not saying these factory made trays are not worth their money... time is money and if i count the hours i worked on this thing at and take research into account, plus the quality of the work on the factory dams than i think the price can be justified. but than again some free time spend in an enjoyble way could yield something that does exactly the same for a fraction of the prise