It's iffy. I drove with two Rovers on the back of the Explorer through heavy rain and flooded country roads once I got near the coast. Both bikes got SOAKED between the heavy rain and 2' flooded roadway splash a few times. I let the bikes dry off over night in the tent and half the next day.
I covered the handlebars and battery port on both bikes. While one bike had zero issues - the other bike sadly developed a ghost throttle and a mind of its own. I explained the situation to Rad and they didn't seem concerned about the wet weather. But I'm thinking the rain got somewhere it shouldn't have. Replaced the controller with same issue. Replaced the wire harness and the issue went away. Was it the cause of the rain?? Who knows.
However I think they are fairly waterproof but anything is possible. I'd cover them with at least a tarp. I went online to Amazon.com and ordered a 4-person instant tent and it stores both Rovers perfectly with a bit of room for extra gear bags. Not a bad deal for $89 shipped prime.
And we made some 3D battery port caps. This way when you remove the battery you can cover the connection port with a water tight cap. Naturally it will pool water in there and if you go to plug a battery in - you could have a boom boom show.
I've been looking for a while for something to cover my handlebars when traveling. It for a short rain storms or really dusty roads when on the back of my vehicle. I ended up using Sarah wrap and some duct tape for now when heading out of town; but, that looks all cheap. I also have a travel cover I can use to encase both Radrovers on the hitch at the same time (folds down to a size of twin bed pillow).
I saw a few sites that make handlebar covers and they are mostly from overseas. Not 100% sure if they would fit the Radrover or even worth the price?
I have a 7 seat SUV and it is a travel bike cover with semi transparent windows on both bike wheels for tail lights. I only use it if there is an unavoidable storm or I cover the bikes on the road at the Hotel. I can't see out the rear window and it feels like I'm dragging a parachute at +65mph. I just don't want the Radrover to be hit with rain at that speed (like washing your entire bike with a high pressure hose for hours). The one I have can fit around both RadRovers and my Saris bike rack completely with plenty of built-in cords to tighten it down.
I saw a lot outdoor covers on Amazon for 1-2 bikes that fold small enough to fit in a rear bike bag or toss in the back of the car when needed at the campsite.