Here are some pics of the weight placement and the DURANGO outdrive boot covers I use. They fit the tamiya outdrives perfectly on both sides and keep the grease in and the rocks out. For these boots to work best you need to put a very small dab of CA glue on the shaft side to keep them from working their way back off.
First Pic - Losi weights (not a "blue" solution for you Tamiya purists - but do the job).
Second pic - The Durango outdrive covers (you can buy these anywhere). Again, not Tamiya blue, but fully functional.