You've gotten lots of good advice, and some very viable alternatives to mounting your antenna to your house gutter--I really like the Ventenna--great for communities with those pesky covenants.
That said, sometimes you just have a pile o' stuff in your basement, and you want to fiddle around with it. Here's how I mounted an NMO antenna to my house gutter in the days before I finally put up a dedicated scanner antenna mast.
The key was to reinforce the gutter lip--which was far too flimsy with the original gutter spike--with a snap in/screw-into-the-roof gutter hanger. The gutter hanger really stiffened up that section of the gutter lip. Once that was done, I just used an L-bracket with some substantial metal screws, and added an NMO mount. Make certain that you add a lightening/static arrestor to the coax, and ground it all.
Just one final note, I don't think that my method would handle the weight of most discones. If you're determined to use the gutter method, I'd recommend a multi-band, NMO scanner antenna--one of my favs is the Larsen 150-450-800 mobile antenna--it's very good across all the bands.
Good luck with your move.
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