I totally see what you are saying re: ground rules that we all have to live with...I have to pay my taxes in the next couple of weeks.
With teens, it is time for them to feel like they have some of the control. What if you had a sit down with him and tried to create a set of rules for the family that everyone is happy and comfortable with. In our home, check in times are 3, 6, 9 and 12. That doesn't mean that they have to come home, they just need to check in. At this point in their lives and certainly when they start driving, I really can't tell them where to go or what to do. But, drinking and driving, for example, is unacceptable. If there is drinking going on at a party they want to go to, then the car doesn't leave our driveway. I won't forbid the party, but I will keep the car keys. Hopefully they will not choose to be drinking underage anyway...but I can't make that decision for them.
If you work together on creating groundrules, then your teen is more likely to follow them, because he feels some control in his own life.
Regarding the fort - I agree with pp, have a sit down and come up with some solutions to what you see as the problem. Maybe your guy truly doesn't understand what the issues are. Purchasing his own TV (battery operated so that no electricity is needed) could be a good option. If the household tv is borrowed, perhaps it could be rented to your teen which would ensure that if it become ruined due to weather, you would then have money to purchase a new one.
I am a little bit confused.
It sounds like you have a really good kid- good grades and basketball indicate that he handles responsibility well. Same friends for years - probably you know them well. So, why is he gone for the whole weekend?
Could you just go get him and explain that you have been worrying and that you miss him? Maybe you could welcome him with lots of love and empathy and then really talk to him about what is going on. IMO this is a great opportunity to have a fresh start because he will be assuming that you are going to lay the hammer to him, but instead you will show him that you understand where he is coming from...
You could even apologize to him because although you have been a teenager, but you have never been the parent of a teenager. You are learning too, and you hope he can understand that and forgive you if you come on too strong at times.
When he uses profanity with you - just tell him that you expect to be treated with the same respect you give him and you will be happy to talk with him when he treats you with that respect. Then walk away.
All items taken to the fort the belong to the family - he needs to find ways to earn money for those items. If necessary you can sell his xbox, etc. to pay for those items. Hopefully he will choose to either pay for them or bring them back on his own.
Good luck during this time. It really does sound like he is a good kid.