You just need to get better equipped. If you have the room to do it on the floor, you have room for tables.
I have 4x12 tables, same height, on wheels that I can move around for large stuff. We made the tables ourselves, welded steel frames with MDF tops and cutting mats. Probably a worthwhile investment if you're going to get into those. Yes it's easier, but even if you have to do it on a floor, I think you're over-thinking this, it shouldn't take long just to trim. We trim a lot of graphics, banners, flex faces in the field if they need it to fit, in parking lots, on grass, floors, beds of trucks & trailers...
I do flex faces like these, I can trim a full roll down to 26x6.5 feet in minutes, plus weed, mask, lay the black vinyl in about the time you think it'll take just to trim those.