spacer for 0.8" thick home heating furnace panel air filter

My furnace has a blower fan with an 18"x19" opening. The standard size panel air filters are 18x18 or 18x20. 18x19 filters cost 3x as much since they are custom order.

So I designed a spacer that wraps around the edge of the panel filter to fill up the gap so the blower doesn't get clogged with dust.

You can scale this for any sized filter.