For 1/48 aircraft, I drill a hole for a #8 or larger bolt in the belly between the wings. I run the bolt up through a hole in the wood base and secure it with a countersunk nut on the bottom. Then I put a good glob of 2-part epoxy on the other end of the bolt and insert it into the hole on the bottom of the model.
Unfortunately, this is completely irreversible so I can't recommend it for all! But it will never fall apart!