Welcome to the forum! Good luck with your new project!! Decking should be fine, just make sure there is enough air circulation so your wood does not rot.

Are you going to bolt it down? You dont want it taking off in the wind lol....

I would treat it with some wood preservative, cuprinol or something.....

Recycling tubs, great for growing cauliflowers in lol.........easy to make cloches for