LDPC convolutional codes have been shown to be capable of achieving the same capacity-approaching performance as LDPC block codes with iterative message-passing decoding. Here, asymptotic methods are used to calculate a lower bound on the free distance for several ensembles of protograph-based LDPC convolutional codes. For these ensembles, we find that the free distance grows linearly with constraint length and that the free distance to constraint length ratio of the LDPC convolutional codes exceeds the minimum distance to block length ratio of corresponding LDPC block codes. Further, building on work by Abu-Surra, Ryan, and Divsalar, we adapt the procedure to obtain a lower bound on the trapping set number for the LDPC convolutional code ensembles. This can be used to predict where the error floor will occur for these codes under iterative message-passing decoding.