We do not recommend putting DiamondFinish Clear over RustSeal because although DiamondFinish Clear is absolutely UV stable, DiamondFinish Clear does not block the UV rays from getting through to the RustSeal. Over an extended period, DiamondFinish Clear can delaminate from RustSeal when exposed to prolonged sunlight.
We always recommend a solid color UV stable topcoat paint (such as BlackTop or KBS MAXX) over RustSeal if RustSeal will be exposed to sunlight.
Please check out the DiamondFinish Clear Directions as it is an invaluable resource.