I would suggest an acrylic
(plexi) over polycarbonates like lexan, simply because the acrylics tend to be strong enough and more scratch resistant.
But have you spent any time looking at the totally different grades of plastic that are available? In both acrylic
and poly, there are literally dozens of different grades. Some are highly UV and scratch resistant. Others, which are commonly stocked, ARE NOT.
If your local supplier just sells "plexi" and "lexan" and doesn't mention they can order in many different plastics, you need a better supplier.
I'd confirm the strength of the rest of the hard dodger, then ask a reputable supplier what they have (what thickness) in what material with a similar strength but high resistance to UV and scratching.
A lot of scratching can be avoided by simply spraying down with fresh water
to get any salt
crystals off before wiping. And a lot of UV crazing is actually caused by petrochemicals in polishes and waxes.
A regular washing
and buffing with Nexus series polishes will also keep them looking new for years.