Hi Joe,
Telescopic props generally don't have a safety, but it is easy enough to drill a hole through which a "safety" pin can be inserted.
Andrew has a chart or info out there somehere on geometry or placement of the props.
While some gas shocks are installed so that they constantly place pressure on the hinge, they can be installed so that once the 2/3 closed mark has been passed, they begin to "pull" the hatch closed and put light pressure toward keeping it closed.
I have mine set up this way.
There is no pressure against the hinge trying to push it open.
Gas lifts are $20-$25 each, cheaper yet on sale.
Car parts store are a good source.
While homemade supports may well be cheaper, and you may be plenty strong enough to lift and lower that heavy weight many times each day while camping, what about your wife, or a future owner?
Either way you go, enjoy your tear, and please post pictures of your final setup!
Rob