Dattack- I don't normally weight down the end pieces, but when I put a bottom piece on, I place a bucket or two full of sand across the frame to help drive it deeper in to the base piece. Not sure if it makes much of a difference, but that is definitely the joint to make the strongest.
I have not used #3, I find that #4 is plenty fast for me. Putting the bottom on a 8' tank is a 100 yard sprint already, I'm not sure it could be done well with #3.
Your welcome all.
Zeph