Hi Dave some pics as promised "hope these work ok"

the tools and kit you need

the wheel on the left is drilled out ready to go i used three sizes of drill bit to take the hole out rather than one large one its easier and more accurate

with brass tubing

all ready to glue in place, put plenty of glue into wheel i used the blunt end of a paint brush to work it in

glued in and filed down,when the glue is set i used a 4 mm drill bit to clear the excess glue from the inside of the tube be carefull not to score up the brass too much

finished wheels on the tank, note the small washers to take out the end float of the wheels and thats pretty much it. hope its of some use to somebody i see no reason why this wouldnt work on plastic wheels and it should greatly improve the life of the wheels.all the best Rob