Shop manual has procedures and my best suggestion would be visit the local Lexus parts and take your vin.

Let them drill down to the parts diagram of the section you are working on and it will have exploded view of which part goes where. [In theory you can do the same on your own if you visit the online retailer parts]. The parts department would readily print of the diagram for you. Note: some times the diagram will have notation as to go visit another page or will refer to another diagram so in store visit helps as they can read the abbreviations etc.

You can order the parts right there too.

Salim

PS: If you crawl under, you can see which hole has metal (machine) threads and which need a clip. There are 3 types of clips used by Lexus.

The panels have an order and if you took them off a while back, don't be discouraged as you might have to assemble, disassemble, reassemble to get the right sandwich order [Don't get frustrated and bend things out of shape].