I'm sorry but this is just.............. nuts, JMHO. Or let me explain first; I'm Dutch. Overhere an
ECV is very very much a standard norm. You know the stories about everybody riding bikes overhere and having millions of bikes? Those are true and those of us that can not use a bike will most likely have an ECV. Anybody with a mobility disability basically gets an ECV on our social system unless there is an indication they can not use it. Which results in hundreds of thousands of ECV's if not a million on a total of 16 mln population.
You know the story about England where it always rains? We're neighbours and know the feeling. Rain is a norm in autumn, most of spring, winter (if not rain it'll be snow in the last few years) and with good odds of many rain days in summer. If rain would be a huge problem for ECV's we'ld have a big old problem allright! Even just thinking about the bill for repairs that would come if rain indeed would cause havock (as maintanence is a covered thing when getting an ECV within our social system). I can safely say many ECV's see many days of not staying dry in our little corner of the world. Have a couple of years with that under my belt myself.
Unless they are renting out totally cr*p ECV's, they should be able to handle a normal rain shatter. Sure, the ECV's in US rental tend to be........ off lesser level than what we are used to as a standard down here. However; both levels come with the same way off wiring, openings and what not which doesn't really cause that huge of a difference in what they can handle in "wettness". While it's not advisable to hit each and every Florida baddest down pours for hours, don't take what was said to the literal detail. Don't be frantic about each drop of water, it can handle it.
Now for you as a user having wet controlers might not be the greatest when it comes to having optimal grip etc. A good reason to dry off the controls regularly when finding yourself in rain while not covered the controls. You can easily cover the controls if you are worried by using a simple rain cap that was meant to keep a humans head (read; females hair

) dry. Best are not those with elastic in them (won't adapt all desired shapes to the best) like most showercaps but those plastic ones with ribbons on each side you can tie underneath your chin if you'ld wear them on your head. Easy to use at it is rounded in shape and can easily be put on and the ties can be tied up on the back and it stays put without you constantly needing to watch it or be aware of poncho's moving out of the way when you move yourself. They're dirt cheap, can be reused if you dry 'm, take up no place in a bag. Does come with the downside of being a barrier between your fingers and buttons.