If you are sewing capable. They have boat fabric (pleather) in all types of colors.
If you get 2 large pieces, and then use those tools that put holes into fabric, and then put one of the gold/silver grommets in the holes.
Then bring along some thin rope, strong string.
So remove child. Strap on the pleather fabric. Since its just for the water rides, if youhave it cover the seat, then under the seat, use the string to tie it safely to the seat, but make sure all sides are covered so it doesn't get wet. Then same thing for the seat back, cover it w/ the pleather use the string on the edges w/ the holes to secure it.
Then head to the restroom. Remove kid, get the child all dry, and then remove wet pleather and hopefully you have a dry wheel chair.
I use an
ecv, and need an extra back rest, since I'm so short. Well, its fabric, so we cover the back w/ the pleather cover to keep it dry since you never know when its going to rain. It keeps the backrest from walking off, as we tie the cover on good. It only take a few minutes at the beginning of the trip and at the end. For the back rest, think rectangle. the 2 long sides have the holes down them, then we fish the string thru it.
Maybe it would work for the seat part, if you put elastic on the edge of the traffic. Then it would take less time, all depends on how easy it would go on the seat, and what parts of the arms stick up, and back rest come up from the seat. Think shower hat for the seat.