I'm with mtclifford. A loaded touring wheel built by a reputable shop should do it. When I weighed 250, I'd routinely load 80 pounds of groceries on my bike and not collapse the wheels, and I ride on 32h rims.
A 36h double wall mid-to-high profile rim should be plenty strong. Now, I looked up the iZip and there's 2 models of it: A 26" and a 700c model. Which one did you get? (A co-worker of mine just bought the 700c model and moved the electronics and assist kit to a lighter bike.)
For a 700c rim I would look at the Mavic A719 or Velocity Dyad. You don't need to go as high-end as the XT hub, but it won't hurt any. I fully agree with the DT spokes, but I'm a fan of the straight gauge Champion series. DT Champion 2.0 spokes go on all my builds. The db Competition spokes make for less road vibration and allow the rim to soak some additional impact because the spokes can flex a little more, but I feel this flex when standing/climbing and think the wheel feels "soggy". A straight gauged build is going to be stiffer and transfer more vibration (so run a wider tire), but it will not feel flexy.
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