The first thought I had was that the explosions themselves could be simplifed by referencing to an already existing rule by saying something like "resolve a hit by a grenade with the gas cloud centered on the barrel".
Also, it would be cool if there were other results than explosions, because who knows what those barrels might contain. Maybe if you roll an explosion on the tables you get to roll again on something like;
D6 -- Resolve a hit with the gas cloud centered on the barrel by a Grenade of the following type;
1-4: Frag
4: Choke
5: Smoke
6: Roll a D6: 1-Hallucinogen, 2-Plasma, 3-Photon flash, 4-5-Frag Missile, 6-Roll twice and apply both results
I dunno, I just feel that it would be cool if you never knew what to expect from a barrel when you shot it, and that instead of reinventing the wheel by making a lot of special rules for this purpose you could benefit from using the already existing explosion rules.
Not too shabby, but if you want to make it more realistic and more often used, you could complicate the math a bit. If you are shooting at a model using a barrel as cover, a miss against that character that would have been a hit if there were no barrel hits the barrel instead.
Ex: A standard ganger with a boltgun shoots at a model at long range in hard cover behind some barrels. He would normally only need a 4 to hit, but needs a 6 due to cover. Therefore, on a 4 or 5 he would hit the barrel, and on a 6 he would hit his target. This way you could keep the toughness of the barrels high to show the rareness of your random fire actually doing something, but give a chance for people hiding behind potentially dangerous materials to regret that decision.
Couldn't that be worked out just using the normal Stray Shots rule? Just by treating the barrels as a model. But I totally agree that there should be a way to hit these by accident.