The Juice is already weatherproof. Just don't mount it upside down.
With both reflectors removed, the gain would drop by 2-3 dB across the UHF band. Of course, the F/R ratio would drop to 0 as the antenna would then become bi-directional. I have no idea what the specific effects might be with a single reflector removed. As far as I know, that has never been modeled and I know I haven't tested it.
Rotating the antenna is not recommended unless you're in an area that uses vertically polarized broadcast signals as there's approximately 20 dB cross-polarization rejection. We've made the current production models capable of this rotation as we've been contemplating an entry into the UK market. Please note, there are some TV stations in North America that utilize circular or elliptical polarization so those stations would not be affected by the rotation of the antenna.
It is often to experiment wit the physical location of the VHF dipole. Moving it a few inches or a foot or so can make or break reception, depending on the immediate peaks and nulls present in any signal in any given point in space. Patience is a virtue.