Thanks. Looking at the Sensar mast, it appears it wouldn't be too big a deal to shorten it with a hacksaw and drill. So if I wanted an "in-between" length, longer than the Rayzar mast, but shortened to clear the Max-Air vent behind, that would be an option. A couple extra inches of boom won't be worth the effort, but more would.
I'm going to keep the Sensar unit, so that I can caulk in the crank assembly onto the roof today. Ordered the Rayzar retrofit kit, which hopefully will be in a day or two before we leave next Sunday.