Already commented Ed yesterday I spoke to a tech expert at a company who sells resins etc he recommended an epoxy in their huge range rather than poly resin , he mentioned you drop poly pens they break and the ease of turning epoxy.
I have yet to buy this and some other things he said an ideal temperature for epoxy is up to 25 C otherwise it sets up too quickly and use a 40 minute setting time product. Also extra heat gives volatile reactions in the mix.
What say you veteran of a few now?.
Peter.