*Sigh*
I have to confess that I am starting to get very frustrated. None of the advice above worked for my current shuttle. Attaching the gear to the fuselage and offsetting it only resulted in the gear staying in place while the wing ripped off anyway. The gear was clearly attached to the fuselage, and stayed in place when the wing went flying, so what stress was the wing under to cause it to rip off so easily???
So I gave up on that shuttle, and built the following Mk3 SSTO:
https://steamcommunity.com/sharedfiles/filedetails/?id=2072732104
And the wings kept falling off that one too. I'd accelerate level to supersonic (to get the most thrust out of the Rapier engines), then even the slightest, and I mean slightest (using fine control and an Xbox controller) pull up to start a climb would cause the wings to rip off. I tried a dozen struts, nothing would work.
I repositioned and reinstalled them several times, and one time it finally worked. I looked at the difference - I had forgotten to enable autostrut. With autostrut on, the wing joints are as brittle as glass. However, now on my new SSTO, the joint between the Mk3 cargo bay and Mk2 fuel fuselage is very loose, it jiggles around like crazy when I spawn in on the runway, and it lets go as soon as I pull up too. I had it work once, it was very strong, but then every time after that it has ripped off. But this time at the fuselage, not the wings. Again, the most minimal of pullups causes it to detach, and even on spawn in when it bounces on the runway the joint jiggles all over the place. I've even tried manually putting on several struts, and it still rips off. I'm starting to get very frustrated with that one.
The good news is, armed with my newfound knowledge of autostrut problems, I disabled them on my shuttle - and low and behold, it lands and the wings stay intact. In fact, it stayed intact on a hard landing that it definitely should have come apart. So one problem fixed, and my shuttle should now be good to go and usable. Now I need to figure out why my SSTO is falling apart...
TL;DR: turning off autostrut fixed the wings coming off my shuttle!