And now, another idea on how to perhaps discourage Fast Travel/Long Rest spamming.
Instead of a chance of a random encounter or whatever has been discussed previously, what if you have to spend additional Camping Supplies to both Fast Travel and Long Rest (which would also include Send to Camp functionality). In other words, it would be sort of a Tax on Fast Travel.
So, here's how it would work. Assume the beach is the primary camp, since you can literally Long Rest on the beach. The further you go from the beach, the more Camping Supplies it would cost you to Fast Travel to it and Long Rest (or send something to camp). So, let's say from the waypoint you meet Gale to the beach waypoint, any time you long rest in that entire area, it would only be 5 Camping Supplies extra to do so. However, let's say you travel from the grove to the beach. That's 10 Camping Supplies. From Moonhaven to the beach, that's 15, etc.
However, mini-camps reduce the amount of Camping Supplies it costs to Long Rest. So, if you Long Rest in the Dank Crypt, you have a mini-camp right there. No additional tax to camp there. It's considered an actual Long Rest camp location. Same with Owlbear Cave (I think there's one there also).
What this symbolizes is that you have expended more energy and so forth to travel to the place, so you are more thirsty and hungry than you would be if you camped at a place that is closer. When you Send to Camp, it symbolizes that you had to actually travel back to camp, drop your stuff, and then return to where you were, travelling a WHOLE lot more (so maybe even double the Camping Supply Tax).
Anyway, the details I haven't exactly worked out, but at least that's something to somewhat discourage long rest spamming and fast traveling, providing some form of consequence.