Physics Easing on the Ground

[Display Name]

I'm trying to build a moon mine out of 15 vehicles via couplers, and it goes just fine, the vehicle sitting nicely on the ground, until it gets big enough for physics easing to kick in.  When it does, the whole thing goes bouncy castle and won't settle down.  The longer I leave it, the more the whole thing bounces.  I'd guess there's some conflict where it's treating the couplers as rigid objects instead of letting the whole thing sag a little (I wasn't able to find a perfectly flat surface big enough for the whole assembly, the spot I picked is as flat as I could find anywhere), and they're snapping the thing back into a rigid shape every time it tries to sag.  Is there any way to turn off physics easing?  I'm okay to lose a few fps if it means I can actually build my monster base.