I found when out camping that my generator was getting wet when it rained even if under the caravan awning. I also found it got muddy underfoot depending on terrain, this is my solution.
This is what I carry and it weighs next to nothing.
The frame is made up of 135 deg bends, 90 deg elbows, T pieces and polypipe and cemented together
The feet the genny sits on is made up of two 90mm end caps, one is just a cap, the other has the rib on the rim. A 30mm piece of pipe joins them and they are cemented together. When gluing, drill a 1mm hole somewhere to let the air out. After assembly, drill 2 3mm holes in the corner of the rib to the outer wall for drainage.
This is the frame assembled, the 5 lengths of pipe are just push fit so it can be disassembled.
The genny sitting on its foot pads
I had a canvas tarp made up long enough to wrap around the ends and with eyelets for 3 occy straps with hook ends. These not only hold the tarp on, but also hold the whole thing together. The length over the frame sideways is almost to the lower horizontal to allow for air flow.
The cover complete - I use 2 small galv saddles on the bottom pipe of one end with tent pegs to create a hinge.
I've found that if I place the cover at 90 deg to my van wall under the awning and hinge from the outer end, it hinges without catching, so that I can a. start the genny and b. refuel. The genny electric output is inboard and the exhaust faces away from the van.
It's survived some pretty heavy rain storms, the exhaust end has been splashed with water, but the fuel tank and electrics are always dry.
Polypipe etc - Bunnings, Canvas from a local canvas manufacturer cost $40.