switched power source

I know, I know. I never post until I need something...
I'm adding a Sirius XM unit to my 96 RMW this week. I want a tidy installation, and I'd like to know the nearest source for a switched hot wire. Currently I have the power from the ciggy outlet just so that I know everything works, but it's permanently on. I have a reworked head unit coming with a front "audio in" socket so hopefully it's a cleaner sound than the FM channel setup.
Given that the dash face is off ready for the radio, I can tie in anywhere....is it best to run a wire from the fuse box, or can I tie into the radio wire?
Thanks as always,
Simon

Remote wire on the radio harness will be fine.

Just so that you know, I may not post but I do stalk the forum, and I do try to search before I ask.
Sometimes I need a bit of reinforcement before I jump into a project, so thank you!

No worries. It's a pretty good resource BECAUSE most questions have been asked/answered anyway. Are you adding a standalone XM tuner and leaving the factory radio?

I like the factory radio look, and my first intention was to use a cassette adapter for the XM. Not surprisingly, I'd never used the cassette, and found out it was broken inside. I explored new radios, but many of the double din offerings seemed to have disco lighting colors. I found the remanufactured CD/Cassette factory unit with the (maybe) added benefit of the aux input, and ordered one of those.

There's a small space on the dash just to the right of the steering wheel that looks as if it was made to attach the little standalone XM unit to. Note: even the best damned velcro won't hold it in Kansas summer heat, so it's now bolted in place, ready for the new radio this week....

I use 3M tape to mount accessories like that. I have a cell phone mount that's been on the dash of my daily driver for over a year in Florida heat.

And did I even think of the 3M stuff? Even after putting about ten feet of rubber trim back on the sides of my wagon last weekend? Nope.