jokes aside understanding the causes of behavior leads to ways to channel the behavior away from things such as excessive shopping.
Humans do have an ingrained instinct for hunting and gathering and also nuturing. Modern times have redirected that instinct into ways of generating income and the hunting and gathering has become much more about shopping then acquiring that targeted prey. Of course skills are involved too the most successful hunters have good skill sets.
When a person retires and no longer is engaged in the activities that generate income then sometimes they do turn to excessive shopping for the sense of accomplishment. While there is indeed a reward of acquisition it can have way to many downsides.
So you need to find substitute activities that feed that impulse to hunt and gather. Hobbies can give us those. One easy but challenging and rewarding hobby for nomads is digital photography. Ordinary looking things can become exotic and exciting looking, real works of art. If you publish the photos on social media you can gather lots of rewards in the way of compliments about your skills. Tribal approval instead of approval by a corporate system. There can even be monetary rewards if one wishes to pursue that. There are online communities devoted to gaining the skills to getting extroidinary photos using the cameras built into cell phones combined with free apps for modifying and enhancing photos. Because the results can be stored on very small memory cards it is in many ways the ultimate hobby for a van dweller who is storage space challenged.
Of course if you want to capture a mans attention and lead them into such a hobby make it a challenge such as which one of you takes the best photo of the day. Then have a little reward for that, you will think of something, it can be something very simple such as a giving a back rub, having the other person make breakfast or wash the dishes.
Some people bird watch and keep records, others do vegetation hunting, identifying plants and flowers. Some go mushroom hunting or rock hounding. All of those activities are related to hunting and gathering and come with the reward of "acquisition".
There are also other hunting activities such as target shooting with arrows, slingshots, pellet guns, those are more direct hunting activities but hitting the target is the reward, the acquiring of skills is the reward rather than actually killing something. Fishing is in the category of active hunting and gathering.
So get busy and switch him over to a substitute activity for the rewards that he was getting from online shopping. But do have a discussion about what online shopping was bringing to him and why it would be a good idea to make a change to something different.