3. Trade up to draft one of the big three tackles
Instead, to ensure that the Chargers get an acceptable starter at right tackle, they could trade up to select one of the big three of Neal, Ekwonu, or Cross. That would likely require their third round pick and potentially more to move up to select Cross, as moving up for Neal or Ekwonu would be far more expensive.
While this trade is understandable and would patch the main hole on the Chargers roster, it would help to perpetrate the same problem that the Chargers roster has been pestered with for years - poor depth.
Remember how the Los Angeles Chargers' backups got crushed by the Houston Texans' backups? If you trade up for Cross, you can expect such a game to go even worse next year.
The Chargers need depth, and trading up would likely hurt their efforts to acquire it. However, third round picks are often developmental (see: Trey Pipkins), so it would be understandable to give one up to solidify the right tackle position. Still, other options appear better.