Those bath houses are good! I've seen them - they look fun. Agree with Cypher that the Supreme one is probably safest, but you could maybe put something different in his potty litter tray to save on the sand. Finacard sell this pellet litter called Papelit
Hamster Bedding-Dust Extracted Healthy Hamster Bedding
You can get sample bags to try before buying a larger bag, but the sample bag includes the Finacard substrate and the paper nest material as well. The bit of Finacard substrate could be useful to mix in, but you don't really need the paper as toilet paper is fine for nesting material.
It's £5 for a sample of all three
Sample Pack - £5.00 : Finacard, Quality Animal Bedding
Or £3.50 for a 'mini' 7.5 litre bag of the Papelit potty litter - which sounds like the better buy and 7.5 litres sounds quite a lot.
Mini Packs [Multipack] - £0.00 : Finacard, Quality Animal Bedding
He could still have a separate sand bath but you'd use less sand that way - an enclosed one sounds like a good idea.
I actually gave up giving Charlie sand because he didn't like it much - he also dug it all out and then filled his salt pig sand bath with cosy bedding instead. He does have sand in his potty and he still digs a lot of that out and puts bedding in his potty too.