Almost finished excavating my crawl space. Down to 42" throughout.

The floor joists (some 6" some 8") are placed at irregular intervals. While
some are nearly 24" o.c., most of them are not. Spacing ranges anywhere
from 12" to around 19".
What is the easiest way to insulate (from below) these odd cavities. When I
did some of the walls, I simply used my 36" paper cutter to cut the
insulation and installed the small pieces 'side-ways'. If I made
longitudinal cuts there would be a lot of waste with long thin slivers of
insulation left over.

Somebody must have already solved this. Please don't tell me that
professionally installed foam is the answer. I cannot afford that
alternative.

All replies appreciated.

Ivan Vegvary