Any of the standard 6 foot whoopie slings sold by the vendors here will be fine. For tree straps, 6 feet should work fine as well. You can connect the two via many different ways. You can use a toggle, a Dutch buckle, or a Bloomgorge Elephant Trunk to attach the slings to the webbing.
The common ENO modification is to remove the stock rope and simply feed the fixed eye loop of the Whoopie Sling through the end channel of the hammock and then feed the other end of the sling through the fixed eye loop creating a larkshead. Then just put the webbing around the tree in the same way and connect the sling and webbing using one of the ways I mentioned above.
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