In times of need, a little support can go a long way in helping people. Many would argue that during events such as extreme weather or natural disasters, it is a necessity for those who have more to pitch in and help those who are the worst affected. The only way out is through, and that isn’t happening without some help when you are dealing with the worst luck.
There are not really any etiquette guides out there that have specifically been written with accepting help after a natural disaster in mind, and arguably, there doesn’t need to be. However, this is also the kind of thing that has to be considered on a case-by-case basis. If you benefit from somebody else’s generosity and then are able to get back on your feet, showing a gesture of gratitude can be an important thing to do. After all, it is nice to be nice.