The link to the blogpost in the first post of this thread draws entirely from James H. Bruns' definitive book:

To weave some additional fabric about the Philatelic Truck ... The Truck also sold this souvenir cover which visitors could mail. Mint copies are common, but mailed copies are quite desirable. This one is signed by Truck employee Ralph Davis and mailed from Indianola, Iowa:

A copy of the souvenir sheet can often be found inside these souvenir covers, but in this case, it has the folded order sheet for the Philatelic Sales Divsion:


Bruns also describes three booklets sold on the Truck listing U.S. postage stamps:
The hardback for 75 cents, covering stamps issued through 1936, copyright 1937:

The paperback of the same for 25 cents:

And last, Bruns describes 3 variants of an uncommon "Junior Edition" which sold for 10 cents (Bruns, page 54). The 1938 "Junior Edition" paperback:

The second variant, identical to the first, but containing this loose page 64/65:


And the third variant, the 1939 "Junior Edition" paperback with a slight title change and a few extra pages:
