A tried and true method is to epoxy in some tri stock on each end of the block against the fuselage sides. Another is to put a layer of 2 oz fiberglass on top of the block and run it up the sides of the fuselage. If you don't have either of those handy, a 1/2 inch wide piece of 1/4 plywood or basswood will accomplish the same thing to anchor the gear block to the plywood sides of the fuselage better. You don't want to make it too strong though. If the LG block can't break away a really hard landing on the gear is just going to rip out the next weakest thing which will be the bottom and sides of your fuselage.