Don't forget the potential for the gunner's armor to provide some protection from the backblast. A full-body suit (like a CES) plus a face shield might be enough to do the trick.
Why don't you look at using the speed bonus for a high speed missile as the DM to the KEAP damage from Striker. For example, a missile with a +10 speed DM would get a +10 on the table, slightly better than a Hypervelocity round. I haven't run the numbers yet (left Striker in the car) but it seems reasonable.
