calico20hill this is what I might do... I checked the Portland weather forecast... After next Sunday there's no freezing temps. I would plant the seedlings in the ground. I would water them in with warm water. I would protect them using floating row cover or create makeshift mini "greenhouses". The "greenhouses" would span several seedlings, and be made of lightweight plastic garbage bags, supported by chopsticks or some similar support. There would be ventilation holes to keep from accumulating too much heat under the plastic. The main advantage of the protection would be heating and wind protection, until the warmer weather comes in a few weeks.
Although it's too cold to outright plant tomatoes in my area, before leaving for a week, I had to get my peppers and tomatoes in the ground... And I used some "hot hats", but for those plants that were too big, I attached massive 33 gallon lightweight semi-opaque bags over the cages. It's windy where I live, so wind protection is critical to allow the plants to establish.