Another option might be to use Stan's Notube sealant in a regular tube... Slime works well for lower psi tyres while Stan's makes sealant that works with higher psi tyres and it makes much less of a mess.

On my old Raleigh Superbe I used automotive tyre sealant that I picked up at the local hardware store (cheap) and these tyres can sit all winter without needing to be topped up... I sold the bike to a friend some years ago and he commutes on it daily through the summer and has been astounded at this. This is also a lower pressure sealant and would not use it on higher psi tyres.

It offers puncture protection without adding more than a few extra ounces of sealant.