As described in http://seekingalpha.com/article/2430115-structural-arbitrage-making-money-with-math?page=2
Buy ZIV with 30% of the dollar value of the portfolio.
Buy XIV with 20% of the dollar value of the portfolio.
Buy TMF with 50% of the dollar value of the portfolio.
Rebalance weekly to maintain the 30%/20%/50% dollar value split between the positions.