I would use a hdpe plastic barrels, You can get them for relatively cheap, even get some with the good locking lids. Now I am pretty sure you would want to put in an air vent and such to make sure it doesn't blow up on. When I was younger I was a raft guide, we had some unfortunate events involving rocket boxes being sealed for a little to long.
Um, wouldn't the trash can be out of the sun if it is under a structure? Seems like a removable back panel to shield from sun is a worthy addition in order to delay UV degradation. Similarly, once a bin is full it could be stored in deep shade or even under solid cover.