1) If you go this route, you will have exactly one type of vacation forever: the cabin. It will consume your entire vacation budget with taxes, repairs, utilities, landscaping, insurance, etc, and you won't want to "waste" this locked-in spending by doing something else. That means no beach vacations, no city vacations, no foreign trips, no cruises, no camping, etc. Your "vacations" will be monotonous drives back and forth between houses where you do the same things you've always done.
2) If you'd like to take more of your own things, add a cargo tray and box to the back of your car.
3) If you want to use it on whatever days of the week you want, and you are post-FIRE, why not move into it permanently and ditch the regular house? Note that such a decision might impact the type of cabin you purchase. That is, for a permanent home you might want more space or other specifics. You don't want to get into a position where, post-FIRE, you are paying expenses for a cabin that is not quite right to move into full-time, plus a house you don't really like.
4) You can share a cabin with the extended family right now. Just tell them you're renting a cabin for the week and they are welcome to join in for free. Also, you might be surprised how little interest the cabin provokes in your extended family if they are not already big fans of cabin-based vacations. They might just tell you "thanks for the invite, but we think we'll go to Disney World and spend $5,000 that week".
5) If the AirBNB or VRBO rates per day seem high, contact the owner to see if they would accept a negotiated rate for an entire week or weeks at a time. Much of their cost involves hiring housekeepers, so built into their pricing is the cost of having the place professionally cleaned three times a week or more. If they only have to clean it once this week...
6) Offsetting the pleasant feelings of owning the cabin will be anxieties about things such as forest fires, lawsuits, insurance hikes, broken pipes, vandalism / theft, neighbors clearcutting, road washouts, landslides, etc. Keep the whole picture in mind when visualizing yourself with a cabin and all its hazards.