How to manage rest with changing GMs and players

I have been running a west marches style D&D 5e game where the GM and the players (along with their characters) change between every session. Due to this, every session ends back in town and with a long rest so that players can change naturally. We have tried the gritty realism rest rules to try to make random encounters meaningful but we are still unable to fit more than 2-3 resource using encounters between long rests. This causes our spellcasters to be overpowered as they can use all their spell slots with no risk.

How can we follow the 6-8 encounters + 2 short rest mentioned in the DMG whilst still having some way to hand over each session?

Some ideas that come to mind:

  • Long rests cost gold or something so they don’t take one at the end of each session
  • Players can only long rest every other session or every 3rd session they come to.

Do you have any other suggestions or have you tried any of these ideas and how did it go?