Removing the radar from a mount is pretty simple. If you lift the top/cover, all the connections are either power or signal, no RF. You can just unplug those wires, seal and coil them up, and remove the radar (spelled backwards) dome from the mount. The JRC I have even has some instructions in the manual.
As far as the down angle of the mount, remember that's a wide beam in the vertical angle, plus/minus 15 for the small 2 kw radomes. I mount mine level, and let it go from there. After all, the smallest range is 1/8 mile, and the boat would really be on a steep angle to miss that. If your boat comes up on a steep plane, 5 deg down should do it. In fog I go pretty slow, so the boat doesn't point towards the sky.
Boris