Start/End includelets for content might conceptually work, but it'd be a bit fiddly as you'd also need one between each column, and there'd need to be some settings for the column widths.

So in fact you'd probably need a 'row start', 'row end', 'column start', and 'column end' and put them all in the right order with the correct configuration settings, which is probably more complicated than the Raw HTML includelet solution.

Using Raw HTML includelets as outlined earlier in this thread would work fine, in the situation that you want two columns on wide screens with one stacked above the other on narrower screens.

For more info on how rows/columns work in Bootstrap you can have a look at the documentation here. In essence you need to start a row, then put in all the columns with appropriate widths, then close the row.

Thanks

Joe