Side Table for UDS...Polyurethane?

Yes, it will crack. I like to use 100% Tung oil for outdoor finishes.

how about something like this? http://www.tapplastics.com/product/plastics/cut_to_size_plastic/hdpe_sheets/529

I use this, [ame="http://www.amazon.com/dp/B0006D50RE/ref=twister_B00GHMSQ56?_encoding=UTF8&psc=1"]Amazon.com : Lifetime 28240 Height Adjustable Folding Personal Table, 30 by 20 Inch, Almond : Folding Tables : Patio, Lawn & Garden@@AMEPARAM@@http://ecx.images-amazon.com/images/I/41hS8Tg6fWL.@@AMEPARAM@@41hS8Tg6fWL[/ame]
It is very convenient and I use it for more things than I thought I would.

I agree that some polymer would be a long term no maintenence solution.
I would NOT use that white pvc board used on exterior of homes.