formatting in theme(add div with php?)

I’m developing a child theme from twentythriteen. I have a nice page laid out in CSS, gallery on the right, text on the left.

.entry-content > p{
display: inline-block;
width: 40%;
vertical-align: top;
padding: 0 10px 0 0;
color: #aaa;
}
.gallery{
display: inline-block;
width:60%;
vertical-align: top;
}

Looks great, except when I put a full line break in the content text and then end up with 2 or more paragraphs–>design breaks.
If I thought about it long enough there might be a CSS solution, but it might involve absolute positioning, something I’d like to avoid. Instead I’d like to add a wrapping div around all the paragraphs being pulled in. I figure I would do this in content.php, but my php is weak at best and I’m not even sure how to start. Any ideas?