There are 3 options for the layout of the ErgoTravel. They account for 4 unique configurations.
With this option the 2U key will be on the left or right with the 2x 1U keys on the other side. Note that some Planck Keycap kits will not have enough 1U keys to support this layout. The 4 1U macro keys on the inner columns may be left out.
With this option, you will only use 1U keys and will not require stabilizers. Note that many of the Planck Keycap kits will not have enough 1U keys to support this layout. Only the larger kits may be able to support this layout.
If you have pre-selected your layout, you will want to find a keycap kit that has enough keys for your layout. Below are examples of kits that could be used for the supported layouts. You may have to compromise on color or keycap profile.