Hey kiddo. I grew up without a dad, too. It's hard sometimes, and people, especially some family members, don't know what to say/how to treat you. Here's the deal though, adults are dumb, and they don't know how to control themselves when it comes to bad/strained relationships where kids are involved.
Just look at how some parents bad mouth the other parent in front of the kids. They don't control or channel their anger and it spills over, and the kids bear the brunt of it. It sucks. It isn't fair. It isn't right.
Please understand that this has ABSOLUTELY NOTHING to do with you. It has to do with a grown man excluding a kid that plays no part in the dynamics of the relationship because he has no idea how to control himself.
If you REALLY want to go camping, find a friend that was a Boy Scout, or ask your mom to sign you up for a local big brother program or a local survivalist or camping group. I am SURE there is a guy who will be more than willing to add another kid to his own kids and take you under his wing. (Just make sure that you have a thorough background on anyone you spend time with).
Again, I am so sorry this is happening, and just to say it again, THIS IS NOT ON YOU. If this wouldn't have happened, I'm sure your "uncle" would have done some other boneheaded thing to further alienate himself from you and your mom.
As I said, adults can be REALLY DUMB. Lots of hugs to you.