I truly believe tying down a bike in a trailer begins with a good self locking wheelchock, using a self locking wheel chock you can load and tie down the bike yourself.When the front wheel locks in the clamp the bike will stand up by itself.The model I use and sell is called Bike-Pro ,but there are many others on the market
Below is a picture of the poster I leave on the wall so that customers can see different illustrations on how to properly tie down a bike