Lowering Aluminium Door Frame

[Onoff]

The garage door, a reclaimed aluminium front door has always been a pita. Traversing the threshold with things like mobility scooters, always a mission resulting in it being bent over the years. I'm wondering can I do away with the wooden sill and just drop the ali frame down onto the black DPC? Ideally I'd like a level threshold. Not quite sure what the clear plastic is, the DPM maybe?

 

View from inside:

 

 

Then from outside:

 

 

 

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