I have no experience with the Skymaster tires but helped a friend of mine solve his air leak problems on a FEJ 1/6 scale F-18 with the following:
Buy some cheap foam tires about the same diameter as the air filled tires.
Remove the foam tire from the rim and then trim it to fit inside the air filled tire. We used a band saw and a belt sander to get it to fit.
Install the Skymaster tire (with the insert installed) onto the wheel.
No more air leak and had the added benefit of making the F-18 handle on the ground much better