I would generally leave it plugged in. It does not draw much to keep it on float. Do you know what charger or charger/inverter you have? That could drive the answer one way or the other. What do you leave on (power wise) when you put it in the garage, carbon monoxide monitor, propane monitor, refrigerator or any other suspected current draw. If the draw is reasonably low you could plug in for a week and unplug for a week. I hesitate to give a time frame to just plug in, because that needs to be the time it takes to get a full charge (which is going to be dependent on numerous inputs), but generally 24 hours would do it.
What kind of battery is your starter (AGM or Flooded)? Do you have a Blue Sea ACR or Surepower? For unattended locations ,I would lock out the ACR if I was my starter were flooded and not AGM, to be honest I would leave off all the time. I generally only connect and top off the starters about once a month (usually I watch the starter voltage) and then only for about a day.
If you have a flooded starter long times on float will tend to make them loose water, this tends to take a while but the results would not be something I would want if my van was in garage 12 miles away.
My Magnum Energy Inverter/Charger has a battery save mode that it can be set at.