We study the resistivity vs. electric-field dependence ρ(E) of a dilute two-dimensional hole (h) system in SiGe, on both sides of the crossover from weak to strong localization at B = 0. Using ρ as a "thermometer" to obtain the effective temperature of the holes Te(E), we find that ρ(E) can be attributed to hole heating. In spite of the strong localization and h-h interactions, the power loss does not indicate any deviation from the density and temperature dependences predicted assuming independent and delocalized electrons. The consequences of these results on the h-h interaction assisted hopping, glassy behaviour and E-field scaling are developed. The hole-phonon coupling involves a limited screening, a deformation potential compatible with measurements at larger densities and temperatures, and a piezoelectric component which is definitely probed.