The spokes and spoke tension aren't the only issue. Stock rims aren't usually very strong either, and they can and will contribute to spoke breakage. OP, I'd recommend having wheels built. Velocity DeepV and Dyad hoops are Clyde favorites. I had my 36H F/R DeepVs built by prowheelbuilder.com using White Industries hubs and 14Ga DTSwiss spokes and brass nipples. Bomb proof so far! I weighed over 400lbs (now under 260) when I started using them and they have been absolutely trouble free. They also weigh less than the stock 16/20 spoke wheels I replaced. Get some wheels built and you won't have any more issues.