I don't do road trips anymore but everytime I'm at a bank for whatever reason, whether a box pickup or to do actual banking (lol), I glance in the teller tray. Honestly, I've had some good luck. The best time being looking down and seeing just tons of silver, quarters and halves. In that case I just asked if I could buy the halves and quarters he had in his tray, and he said "do you mean these ones (pointing to the silver)? they're silver so you might want them, some guy brought them in here and said a pawn shop told him they weren't worth anything

." my guess is that he picked one representative coin to show them which was clad, and assumed none of his 'older' coins were worth anything. Anyways, most of the time I see nothing, so I would never bother to ask for loose coins that I can't see, chances are they are duds. However, if you have a good eye, you can grab teller tray silver about 1 out of 20 bank stops. usually the lonely quarter or dime. I don't try to pull one over on them, I just say "hey, can I buy that old dime in your tray, I collect them." nothing is worse than putting on a rouse, just be honest. But realize you don't have to say "hey I see silver in your tray, can I buy it that's worth a lot and I hoard them and...!"
Straightforward and nonchalant wins the game, you DONT want the teller to think THEY lost out by selling you a coin, you want them to feel good about helping a collector. And remember, last word of advice about teller tray silver. If a teller collects silver, it will NOT be in their teller tray, but will be hidden somewhere. so if it's in the teller tray they'll always (at least almost) give it up. Also remember, WE are crazy about silver and silver coins, the rest of the public doesn't see it the same way, and often will give them up with no problems, as long as you don't make a big deal of it.
Happy hunting! work on spotting those dimes! and no I haven't found a war nickel yet, but I'm pretty sure I spotted one in a tray once and I didn't ask for it because the tellers were busy counting my half boxes, and at the time I was finding a lot of 40%ers and figured it wasn't worth annoying them for a fraction of the price of a silver kennedy