Secure the Drybags with straps
You have two options to attach the bags to your bike.
The simplest one is to work with lashing straps. Bikepackers love it. The Santos Drybag has loops on one side through which you can pull the straps almost over the entire length. This allows you to choose almost any place on your bike to mount the Drybags. Favorite ones are the front fork, the down tube, the bottom of the saddle and the rear forks.