Go to craft supply store and buy a 1/8" paper punch. Gather some tin tank scraps together. Take a 1/8" hole template and with a sharp scribe or straight pin, make a bunch of circles on the material. Take a 1/16" drill bit, or a piece of 1/16" music wire with a chisel point on one end, and drill through the circles you just drew. Then take hole punch and punch out washers. make as many as you need allowing for some to be lost. Alternative is to fins some scrap small lip seals that are used in machinery and such. Inside the lip part is a spring, that can come apart. Cut into small lengths you have something like the old spring keepers that Perfect used to market. Work those on and a dab of glue or solder can hold them in place. Thin copper wire can be wound around the axle and then soldered or glues in place. Lots of ways to hold a small wheel in place including 1/16" wheel collars from Dubro!
Type at you later and HAPPY HOLIDAYS!
Dan McEntee