I just saw in the Distrowatch comments that you may need a hand setting up a repo for this. There are a few options that vary in the degree of time/effort/cost associated therein.
1. It's ridiculously easy to set up a repository in Dropbox, but I rather seriously doubt you'll be using this option due to you already capping their transfer limit. There's an article over at peppermintos.us that describes in detail how to do this.
2. The second easiest way is to set up a Launchpad PPA. This isn't the most professional looking of options, but the PPA system is positively fantastic for repo hosting. Make sure your packaging skills are up to snuff as it'll reject anything that's not spot on when it comes to your build process (I like this because it keeps me from cutting corners on anything). The downside is that lots of people use their build system and if it gets backed up you can potentially have to wait a while (this is generally only an issue right before Ubuntu drops new releases). Peppermint uses Launchpad for it's repositories.
3. You can also use a package called reprepro to host your own repo on your own server. It'll need to be a Debian/Ubuntu/derivative system as it's quite a pain to get reprepro installed on anything else (though it's certainly possible). From there just make sure it has a public facing webserver and use similar instructions to what was described in option 1. Reprepro isn't picky about how packages are built so as long as you can somehow squeeze it into .deb format you can publish it (though it's highly recommended you following proper packaging standards anyway). Linux Mint uses hosted reprepro for it's repositories.
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How exactly are you going about building your .iso images? Also, Mint has a lot of built in tools to make package building fairly painless. Since your coming off of Mint 9 Fluxbox all of this will be there from the get go. The in house tool at Mint for building .iso images doesn't seem to play nice with Mint 9 Fluxbox so I "hand built" the release off of what was originally Lubuntu. I have some build notes if you need them.
1. It's ridiculously easy to set up a repository in Dropbox, but I rather seriously doubt you'll be using this option due to you already capping their transfer limit. There's an article over at peppermintos.us that describes in detail how to do this.
2. The second easiest way is to set up a Launchpad PPA. This isn't the most professional looking of options, but the PPA system is positively fantastic for repo hosting. Make sure your packaging skills are up to snuff as it'll reject anything that's not spot on when it comes to your build process (I like this because it keeps me from cutting corners on anything). The downside is that lots of people use their build system and if it gets backed up you can potentially have to wait a while (this is generally only an issue right before Ubuntu drops new releases). Peppermint uses Launchpad for it's repositories.
3. You can also use a package called reprepro to host your own repo on your own server. It'll need to be a Debian/Ubuntu/derivative system as it's quite a pain to get reprepro installed on anything else (though it's certainly possible). From there just make sure it has a public facing webserver and use similar instructions to what was described in option 1. Reprepro isn't picky about how packages are built so as long as you can somehow squeeze it into .deb format you can publish it (though it's highly recommended you following proper packaging standards anyway). Linux Mint uses hosted reprepro for it's repositories.
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How exactly are you going about building your .iso images? Also, Mint has a lot of built in tools to make package building fairly painless. Since your coming off of Mint 9 Fluxbox all of this will be there from the get go. The in house tool at Mint for building .iso images doesn't seem to play nice with Mint 9 Fluxbox so I "hand built" the release off of what was originally Lubuntu. I have some build notes if you need them.