I replaced the front roof vent lid with the official Winnebago part, which is not cheap, but it actually fits.
I put the MaxxAir vent hood on the front vent. It went on without incident. It is held in place by some aluminum brackets that have to be bolted into newly drilled holes in the sides of the vent frame. The hood is then bolted to the brackets. It really doesn't take long, just as the manufacturer's video shows.
I used a Fan-Tastic UltraBreeze hood on the rear vent over the bathroom. The previous owner had installed a new Fan-Tastic roof vent with a high speed fan and I found that some folks say that one really needs this slightly larger hood in order to open the vent a little higher and provide better air flow. The UltraBreeze took a little more time and trouble, in that one must scrape the caulking putty off four of the screws in the vent frame, squirt a little lap sealant in the holes, and then screw on the four brackets using those holes, with a little more lap sealant after that on the screw heads, etc. After that, the hood sits on pins on the ends of the brackets and attaches with a spring cotter pin. Again, not difficult, but a little scraping and caulking is required.
The only mishap was that I managed to crack off part of the little roller/washer that fits in the stock Winnebago lid track and raises and lowers the lid. Since the roller is now flat on one side, it does not work as well as one would hope. I suppose some day I will drill out the rivet and attach a new washer/roller unless there is a better solution.
Photos to follow.