@ozzy
I’m a fan of the springs as well. I guess my main point was the word (overkill). Four minis, IMO may work better than three Ultras. The 45lbs is at the very, very low end of the weight limits for the Ultras. I recently bought some DH Labs cones. I'm very impressed.
Whatever works...works. It just seems that something that will drain may be the best alternative. Good luck!