Won't make it impossible to load a bike. The rear rails are usually hindged. IMO, when i was in construction, I was WISHING I had a full on ladder/lumbar rack. Ratchets bolted to the rails. 2 or 3 ladders on one side, 400ft of 20' sticks of copper tubing or abs pipe. If you know your only going to need one ladder, then do it. BUT, i'd first check out craigslist. You can get a full on rack for cheaper than the one your looking at. Ones with "over the cab" length.
Ever thought about having a headache rack built?