It would be cool to see the “modification” system expanded. At the cost of encumberence etc I could easily see the use case for reinforcing with plastic for acid resistance and/or waterproofing (tallow/wax treatment?), nomex for fire protection or sewing on bulky but convenient pockets to improve volume.
I’m not sure whether your current system is formulaic or would require hand tuning values for every item but this could be a way to enrich the “cobbled together” philosophy and improve player choice. I could easily see one making “poor man’s” bulky survival gear by opting for all the options on a trenchcoat.
While we’re at it, if I recall there are environmental and acid resistance numbers. Is the same true of fire resistance or is it a tag? It would be nice to see all the numbers as a player if there is any variation there.