Who ever you choose to make your custom cover get Top Gun Fabric it is by far the best fabric for boat covers hands down, most if not all shops that do custom covers will have Top Gun Fabric.
Erichsen Marine did mine as well and he uses the poles to hold up the cover inside the boat. I am not a fan of the poles I have had problems with them not standing up and that is when you can have problems with the snaps coming off when you are going down the road. There is a place in Rochester “Custom Canvas” that uses Top Gun Fabric but instead of the poles they use the wooden slats that run across the boat, they sew in a sleeve for the slats so they stay in place. If I had it to do over again I would probably go with the slats. Also my cover ends at the splash well (does not cover the motor) this is the only way to go IMHO, when you cover the motor it wears on the finish of the motor when traveling down the road.