Can you do:- a rolled (safe) edge? Maybe
almost 180 deg to allow for painting inside lip. Could be an option for the outside edge rather than an upstand or down ward lip of 90 deg.
- A 'set' on the front edge would be nice to lie on top of the lower lip of the bumper so that the bottom is flush.
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I think demand would have to be assertained as to what is the popular design. If individually hand made like this, you could cover a whole range of options with regards edges, sides, drain holes, function etc....