Thanks for the replies.
I know that everything will eventually freeze and I know my question has too many variable for a correct answer. I figured (maybe incorrectly) that if I knew how long it might take a 30 gallon container to freeze up (no insulation, no heat added etc) that I would have a benchmark on when I should get seriously concerned about applying heat or dumping water.
Drain pipe valve and the small pipe running from the tank to the pump are something that need attention. Insulating those might bring them back into line with my original question which boils down to something like .... if it got down to 32 degrees in PDX how long would it take a 30 gallon RV water tank to freeze (assuming the RV interior temp was 32).
Thanks.