By chance I had these mini-z foams.
They are in fact sold as a complete cylinder and you have to remove the inner part wich is pre-cut. I drilled and shaped that
First I needed to drill the centre. I used those stone conic dremel bits to do that.
Then mounted the wheel on the dremel using the Dnano rear hub and a metal axle.
Finally I used dremel bits to manually remove the excess thickness to the correct diameter and to round the angles.
For the front I used the stock rear tires wich are shore 10. I don't know if this combo will be any good on RCP but for carpet it is just perfect.