I'm putting a small 30x30"shower in the basement. Id like it to be curbless so I'm cutting 30x30 into the slab (drain trenches over to sump and ejector pump). Can i use kerdi drain with a trimmed kerdi pan...and avoid having to pack the mud slope? The dirt under the slab is firm dry clay. Could i put down crushed rock or sand over dirt to make a base for the kerdi pan? Or pack mud flat over dirt? Maybe premade pan not recommended here? Thanks for any guidance.