Anything you do that exposes raw chipboard or mdf, waterproof it by sealing with aluminium tape. Also all the mating joins between units, back and bottom. use silicone sealant around all internal joints of the sink cabinet, especially the bottom panel and at least 2" up the back panel........you WILL have leaks which will destroy the finish or the cabinet if you don't. If you have a built in dishwasher, use aluminium tape on the cabinet sides and front edges of the adjoining units, and underneath the worktop....otherwise splashes and steam will make the edges swell.
Instead of the stupid legs and kickboards Ikea supply, which your maid will ruin, I used 9mm foam concrete blocks on their sides. This allowed for wiring and plumbing in a space between blocks. Use a bituminous damp barrier on top. The blocks are fixed to the tiled floor with "no more nails" type adhesive (easier to remove and less likely to slip than cement) and the cabinet bottom similarly fixed on top. The front of the blocks is tiled, giving a waterproof, durable and attractive finish...and cheaper, too!