if you use kevlar or nylon for anti-spall on your plates you need to make sure you wrap your plates in the fabric. with fabric bending over all edges and held securely so it doesn't unravel. fragments move parallel to the surface of the plate when projectile strikes it. simply putting fabric in front of the plate won't protect your chin and neck area from spall.
as far as bed liner - i don't think it's that great of a solution for DIY. it works well enough and there are evidence on youtube. however you need to put a lot of layers of it really thick coat and with the price of spray can kind being fairly high - you are looking at significant cost. it's cheaper to buy plates already coated then putting spray on yourself. unless you work at bed-liner application shop and have access to it for cheap.
also stuff theyspray in the shops not the same stuff they sell in the cans. spray can bed-liner is very thin and will take dozens of coats to build up a substantial thickness enough to act as spall-guard.
there is a guy or two on the internet that sells kevlar sleeves to put your plate in. not cheap either but if you already have a bare plate and need SOMETHING still worth buying.