I went with the RB3 type, rubber shielded and sealed, no maintenance other than cleaning the wheel area. I am sure the others would work as well, these are listed as good for dirt application and well sealed but this produces more friction. They work fine on my Sherman and are fairly cheap. Things to note while constructing the Sherman is to use generous amounts of zap ( medium ) while assembling the suspension cylinders, they should be painted before assembly. Use the Tam grease on the parts that move or slide inside each other to make the action smoother.