Let the trust fund invest a TINY percentage say 0.01% or 0.000001% or somewhere in between of the taxes it receives, in stocks and/or bonds. For preferred shares and bonds, some criteria would need to be set up. But for common stock, the company would have had to be in existence for over 25 years, and have paid regular dividends for over 10 years, without missing any. The dividends would have to have been raised over the previous 10 years, amount and frequencies to be determined. A maximum of 1% of each Month's available funds can be invested in a company’s common stock; 1.5% for common, preferred and bonds combined. No more than 1% or 2% of the company’s common or preferred stock or total outstanding bonds can be purchased.
These criteria will pretty much make sure that in the long run, that the money is safe, and the Trust Fund’s investments do not distort the market. Also, just because a company meets the requirements, it does not mean that the investment is required. Some thought must be taken as to prioritization of investments, which investments to make or not invest at all. Dividends would go back to pay current benefits, except that funds are fungible, and should be accommodated. At some point the trust fund may have to start cashing in but that is also to be determined. The Trust Fund should set up an account with Schwab, and/or E-Trade, etc. to cut down on the trading costs.