Modify your table structure so you have each box contained within a table and each of the 3 tables are contained within a single row separated into separate columns. Leverage cellpadding on the inner tables And cellpadding on the parent table to achieve the required spacing rather than using an empty space or set dimensions.
Assign dimensions to nothing other than the total width of the parent table. Make sure you have table, table td:border-collapse:collapse; in your CSS and all your tables are zero'd out with border=0, cellspacing=0, cellpadding=0 (except for wherever you need to adjust the padding.
Place your images and text within td's and nothing else. If your using a paragraph or header tag remove it.
If you structure your table in this way it won't wrap until you want it to.