It's been about 6 years now since I last had a gerbil, Gareth, who was a solo male I fostered initially, but there was no way he was going anywhere :)
He was in a largish glass tank filled with layers of straw, peat, straw, peat, etc. This only needed to be cleaned out once every 3 months or so. It was a bit of an operation to catch him as he'd been accidentally "free range" before the rescue was called out to capture and rehome him, so he was never happy being handled, but I basically just started digging and as soon as his head popped up, I grabbed him! He loved the tunnelling and although he wasn't "tame" and wasn't in a pair/group, seemed to be about the most content gerbil I've had.
I'd had gerbils about 6 years before that and they were either in wire cages or plastic tanks but always on sawdust. I didn't realise now that the scratching in the corner they did on sawdust was a sign of boredom/frustration because they wanted to be digging tunnels and couldn't. Some gerbils also bit at the cage bars - even ending up with a bloody nose - again, signs of boredom from not being in an environment even close to their natural one.
I don't know what the current thinking is (I'd not go by what a pet shop says though - I'd look at gerbil forums and gerbil keeper websites) but I can say the peat and straw in a tank method did make for one very happy gerbil.