I have a 2009 Winnebago Access motorhome that is rarely used. I had a battery tender but it stopped charging the battery. I purchased another tender & enclosed it in a small plastic storage box. In an attempt to protect it from the elements, I then set the box on the tire of the motorhome prior to attaching it to the battery & plugging it into an outlet. The tender has stopped charging the battery. I am presuming the tender can't tolerate the elements so I don't want to purchase another. Is there something else I could use so the battery does not die?
Battery tenders convert AC to DC electricity in order to charge the battery, this creates waste heat which needs to be vented to the environment, which is why there will be air holes or slits on the side or top of the tender. If you seal the tender or charger in an enclosure it will overheat and either break or a fail-safe mechanism will cut it off, this is most likely what has happened to you.
Tenders need to be protected from the elements unless they are designed to be rainproof, but one thing you should not do is to seal them up.