Filling building gaps

I am working on building that sets on a flat celluclay base.  In setting the building on the base I find a gap of 1/8 to 1/3 inch between the foot of the building and the base surface.  How can I fill these gaps so the bottom of the building is flush with the base surface?  I have some Squadron filler but questioned whether that is the right prduct to fill these gaps.  Additional snow will be placed at the foot of the builing which could mask the border with the base.  Any suggestions on what and how to do the gap filling?

Thanks!

Leddy