Recently developed transport theories for small-scale solar wind fluctuations explicitly treat convection, expansion, and other interactions with large-scale gradients, while separating nonlinear effects associated with triple correlations of the fluctuations. To close these models, approximations for the nonlinear terms are needed, since exact treatment of the triple correlations is tantamount to a full solution of the turbulence. In this paper we present a framework, based on turbulence theory, to develop approximations for the local turbulence effects that are required in transport models. Two approaches are given, based on, first, Kolmogoroff-style dimensional analysis and, second, a wave number diffusion picture. Further extensions are given, including a unified approach to the Kolmogoroff and Kraichman spectral theories, the inclusion of cross helicity, and a discussion of nonlinearities associated with the energy difference spectrum.