I have to shake my head. People will spend thousands of dollars, usually TENS of thousands of dollars, on a truck and camper, but balk at a $250 set of tiedowns.
I'm sorry, but get your priorities straight people! The cost of a set of tiedowns is CHUMP CHANGE compared to what you have invested in the rig. PROTECT YOUR INVESTMENT! To hell with safety and other people because I know you're sick of hearing about it. If you protect your investment, safety will come along for the ride.
...and a 4x4 beam as a tiedown? No. Heck no. No no no. Holding down some dirt, and holding down a bucking, bouncing, bounding camper are two entirely different things. One of them is a good place for a piece of wood, the other is not. We build houses and barns out of wood because they are not going anywhere. It's bad enough most RVs are framed from wood. We don't need to be securing them to the vehicle with even more wood.
Think about it though, we are constantly fighting with our RVs as they fall apart from being hammered down the road. All the leaks and subsequent rot are due to the fact that wood is not a good material to build vehicles out of.