I´ve designed a lipo cradle for the TRF511.
With the cradle the lipos are moved back to clear the center bulkhead. It is secured with 2 screw. The front screw is using the same hole as the original battery post. The rear screw uses the same hole as the undertray. So no need to modify the chassis. I also use the original battery posts and battery plates. The cradle is 69x47mm, so most saddle pack lipos fit. Will be available in plastic and carbon fibre.
Photos:
http://www.tamiyaclub.com/showroom_model.asp?cid=91712