My old man brewed a pale ale with agave, and though the flavor was extremely subtle to begin with, it added a great flavor as the beer aged a little more (and presumably the hops mellowed). I don't know how much he used, and I don't know if a dubbel is the right platform for it, but I am certainly going to try it in a pils or golden with just a hint of lime for a nice refreshing cerveza for the summer. A little experimentation is definitely worthwhile with it. Good luck.
Secondary: Oktoberfest, German Pilsner, Double IPA,
In Bottles: Lucknow IPA clone, Rough Rider Brown Ale clone,
John Harvard Imperial Stout clone, Hoppy Amber, Witch's Brew (Habanero and Smoked Corn Small Ale), Porter, Dunkleweizen, Dry Stout, Irish Red Ale, American Maple Wheat Ale, Black Wit, Belgian style Wit, Belgian Golden Strong Ale
Kegged: IPA, Saison, Hoppy Brown Ale