I'd have a 36 spoke wheel built up on one of Velocity's toughest rims on a Shimano hub, Lx or Dx or Xt.

Call Velocity USA and they will suggest something that will work for you.

If you have a good bike shop, they can build it up for you. Should go without saying you want top quality spokes,
beefy ones.

You also might consider a larger tire.