Hard coating for foam toroid

["Lau, Gary" <Gary.Lau-at-xxxxxxxxxx> (by way of Terry Fritz <twftesla-at-xxxxxxxxxx>)]

I recently placed an order for a custom 7" x 30" Styrofoam toroid from a
place that makes custom plastic shapes, largely for theatrical props.  They
have a completely computer-controlled milling operation and can make any
complex shape.  They normally work with 2 lb Styrofoam, similar to what
coffee cups are made of.  They could also order 3lb and 5lb foam.  The 5lb
foam is similar to the stuff they make bicycle helmets out of - very tough
stuff.  But the 3 and 5lb options added roughly $100-$200 to the total cost.
I was concerned with the possibility of denting and wanted to make the
toroid as dent-proof as possible, but at a reasonable cost.  

Initially I was told that they would be able to apply a very thick (1/8")
coating of polyurethane.  I felt that such a coating on top of the 2lb foam
ought to make it pretty dent resistant, so I choose that option.  After the
foam was cut I learned that they would not be able to apply it as the cost
would actually be very high.  So now I'm left with a foam toroid with little
protection against dents.

What materials are there that I could coat it with to improve upon its
dent-resistance?  I don't want to mess with fiberglass or anything that I
would have to sand down.  I'm thinking self-leveling like epoxy.  Is this
available at reasonable cost in bulk (quart)?  Is it thin enough that it
could be poured on while the toroid is slowly rotated?  Is the cure time
long enough that I can get the whole big thing coated before it starts
curing?  Or are there other things?  Someone suggested the boating repair
industry may have something I could use?

I will post pictures and details of cost, contacts, etc, to my web site
after I receive and evaluate the toroid in the next couple of days.

Regards, Gary Lau
Waltham, MA USA