Great, thanks guys!
So some nice gasket material in between the steel mounting plates and the aluminum frame. This Mr. Gasket 9615 should do the job well, yes?
I already regret buying a bike with 24" tires hah... hard to find some heavy duty inner tubes or compatible Mr.tuffy, contacted bikebuyers, hopefully they can help.
And as for torque'ing down the bolts until I see the frame crush slightly... is that really a good idea? makes me nervous!