I haven't built a boxer but I might be able to shed some light on the internal structure of the LG mounts...

Basically these aren't used so much to do anything except spread the load from the maple blocks... If you don't fit them you can almsot guarauntee that they'll tear out in a hard landing..

Mounting landing gear in the wing has always been a graunching issue with me.. I'd fit the spreader ply bars, and when gluing, worry more about gluing the webs to the sheeting than to the foam, in fact, if you don't fit the webs, the amount of epoxy you'd need to get a good bond would be pretty horrific. The strength in a foam wing isn't really in the foam....