The issue of whether a cost reimbursement CLIN for travel on a commercial contract is permissible is debatable. On the one hand, FAR 12.207 states "...agencies shall use firm-fixed-price contracts or fixed-price contracts with economic price adjustment for the acquisition of commercial items." Conversely, some argue that simply including cost reimbursement CLINs for travel—which is "incidental" to the Government's basic requirement—does not turn what would otherwise be a firm fixed-price contract into a cost reimbursable one. An alternative is to use a time-and-materials type CLIN (which is permissible for some commercial contracts) for travel. However, that would require additional documentation and higher-level approval. Because the issue is not clear cut (though some may assert otherwise), I recommend you discuss it with your activity's Contract Policy office for further input.