I recently bought one of these:
PKG394HB - bottom one on the page
David's Collectibles Scope Packages
It seems pretty secure, as it has four set screws to hold it in place. However, i have not been able to get out & test it for staying power yet.
The only alternative i saw that wasn't a receiver cover replacement required some drilling & tapping of the receiver & basically mounted on the left & hung over the receiver cover. I have a forward rail on the tapco handguard, but i don't plan to use it at this time.
I have wondered if the "quick release" type mount for the AK (also available on that site) would work well with the SKS. Of the drilling-required mounts, i like it the bestest.