What about using a longtail? I built two longtails for riding with our dog. He would jump in and out when I asked him to. It is possible to atatch a long narrow crate that he can sit in on a wideloader.

I used to stop and tell the dog "go and drink water" when we came to a stream or river. He would do that, dive in, drink water, pee in the water and drink again and then back to ride more on the bike. With the wet fur he did well in the summer (not tropics here) and there is a lot of streams.

https://www.flickr.com/photos/778361...57667337388135