Much of my weight loss has come from dealing with some of the mental parts of the puzzle and accepting that there are real tradeoffs. It's not enough to 'want to lose weight'. I did that for about 10 years and it didn't work. I had to move from that to actually being willing to make tradeoffs in my behavior. My situation (ultimately losing 80 pounds) was probably easier than yours--trying to keep 10 pounds off. Still, it maybe helpful to think and act on your trip with particular focus on how you want to end up.

We discuss somewhat similar scenarios in my WW meetings. There's a lot of encouragement to take the trips, have a good time but also practice the habits you do every day when not socializing. Really think about ways you can do this. Some people stick to their own weight-loss versions of breakfast and lunch. Limiting alcohol as previously mentioned can address a few related problems. Halving dinner portions but still enjoying the food can help too. Making a point to walk or exercise is another common suggestion.

Frankly, despite you mentioning the one big event, let's face it: three weeks is enough time to do a lot of damage to your plan and could easily set you back much further than when you started out. In my opinion, the big event is only one perhaps relatively small aspect of your vulnerable time. It would take a fair amount of planning and mindfulness for me to pull it off. That said, with your weight situation, I think you can "easily" do it ( ) if you don't lose sight of wanting to come out of it no / little worse for wear.

I do mental rehersals of the scenarios to plan more. I have been "held hostage" on rafting the Grand Canyon with meals and beverages provided. They did make nice food including salads. I didn't gain but was doing maintenance by then. No snacking except maybe one organized one or two. With the hiking it was ok. Hope you have time to hike and walk on R.V. trip.