you can always remove the radio, look behind it and track the wire that plugs into the Sirius port. The wire is fairly short and will be connected to a silver and black box about 3 inches square. This is your tuner and the ESN will be on it.
Yes there is a filter. You have to take the back panel off (foot of aft cabin), look up directly above the holding tank and you will see the long white canister. They are aroung 65 bucks thru Ebay.
Did it on my '97 262 with no problem. Just make sure you get the correct diameter gages and that you keep track of all the wires. I did one gauge at a time. There are some good deal on Ebay for Monterey gauges under "Monterey Boats".