.NET MVC Flowing Columns of Variable Number of Checkboxes

I'm presenting filtering criteria to user: they can select multiple value per field so I need/want to present groups of checkboxes.

I'm doing that now and xferring data to/from controller successfully based on the articles I've found (such as this). I've got this: (rows of checkboxes under collapsible headings)

|_Sites_______________|
_ Site A
_ Site B
_ Site C
|_Types_______________|
_ Type X
_ Type Y

But the number of entries can vary widely across clients, so rather than having a looooong list, I want to flow them - and it's OK if the user has to scroll horizontally because they've got so many.

|_Sites___________________________________________|
_ Site A  _ Site with a really long name  _ Site F
_ Site B  _ Site D                        _ Site G
_ Site C  _ Site E

All the references I see use an EditorTemplate given a collection of items (which I'm doing) - but always result in vertical lists.

I can certainly grunt through it and generate all the HTML myself, but I'm hoping there's a more elegant solution. It doesn't have to be an HTML table - that's just my first guess.

Thanks, Dan