It depends on how you are transporting them, but yes DOT can and does inspect private vehicles. All of the bridge tunnels in Virginia make any vehicle with gas bottles stop at an inspection station prior to proceeding( including RVs). I actually got inspected at a DUI checkpoint by a very knowledgeable highway cop....he noticed the 8 tanks in the bed of my truck and wanted to verify the hydro dates and DOT stamps. Funny thing though he didn't say a word about the pistol in the passenger seat.
