If he escaped before nightfall and did happen to get under the trailer he will still be there. Search everywhere. Id start outside and under the trailer first. He will not wander very far for the first day or so. So get out there and look. If he is not within 10 to 15 ft of his tank wedged into some tight spot id be looking under my house. In leaf litter. Under or behind anything you see when you look around your trailer. especially up under the floor boards, under the furnace room, around the pipes..

Keep looking! You'll find him.