The hosts headed into the break 5-0 up courtesy of a first regional try for centre Steffan Hughes, who was making his home debut, before Billy Burns' solo try got Gloucester back into the game.
But Scarlets hit back with a Josh Lewis penalty and Aaron Warren's try handing them the win that keeps them in the hunt for the quarter-finals.
And with the break from RaboDirect PRO12 duties seeing the younger heads get a chance to shine, Turnball urged them to make the most of it.
"Conditions played a massive factor in the game, we didn't play for as long as we wanted in the areas of the field that we wanted to play and spent a lot of time in their half," Turnbull told Scarlets official website.
"We've always used the LV= Cup as a competition to breed younger players. I remember when I was coming through that's where I got my chance to play some rugby.
"The young guys shouldn't be nervous and should grab the opportunity with both hands. They can look forward to next week's challenge and build on their confidence after (this) win."
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