they are most likely aluminum which is a softer metal than the steel of your edges so you may dig an edge in or it could just be sticky but i see no reason why you shouldn't give it a try. Just remember to keep those front edges up
i probably wouldnt do the bench but i was actually thinking about taking off the back rest and putting some hdpe over it, which would be much easier than building a frame.
also i was thinking about using a soccer goal as a jib.
ive thought about the same thing but aluimanim is so fucking soft, and they usally have little caps on the ends but you could just pop them off i guess
we took it from our highschool football field, and it kinda sucked. really slow and sticky and if you have any edges your probably going to stick/get burs.