Have a color copy, front/back of your form 4. Keep it with the gun.
Technically only an ATF agent has the authority to hassle you over your NFA item but that won't stop cops and rangemasters.
Keep a copy with the gun.
In WA you have to have a trust set up to purchase a supressor.
Not true. If a local CLEO won't sign for a suppressor you will need a trust. Unfortunately, while it is legal to own a suppressor in Washington, it is not legal to put it on a gun...