The HI-MaNGA survey is an HI (21cm) follow-up program of SDSS-IV MaNGA galaxies using the Green Bank Telescope. We combine the derived global HI properties with MaNGA IFU spectroscopic measurements in order to examine the relationship between HI-to-stellar mass ratio and the average ISM properties of star forming galaxies. Consistent with previous work, we find a strong relationship between HI fraction and gas-phase metallicity, but very weak correlations with average ionization parameter, electron density, and Halpha surface brightness. We find HI fraction to be very poorly correlated with integrated Halpha equivalent width, and discuss the implications this result has on the link between galaxy HI reservoirs and star formation. In contrast, HI fraction is well-correlated with oxygen equivalent width, and we discuss how this is likely a natural consequence of the gas-fraction vs. metallicity relationship. HI fraction is also positively correlated with the [O I] 6300/Halpha ratio, and those galaxies with elevated [O I]/Halpha have longer HI depletion times. We will argue that these results suggest the most gas-rich galaxies have larger diffuse and/or shock heated HI components. The scatter in the HI fraction versus oxygen equivalent width relation is also correlated with [O I]/Halpha, as well as Halpha surface brightness, which again imply that the scatter may be linked to variations in the relative fraction of gas in a diffuse versus dense phase.