How is opposition to a TTIP agreement a reason for advocating leaving the EU?

One of the tenets of the 'out' campaign is that leaving the EU will enable the UK to increase trade with countries such as the US - indeed it may be necessary to do so in order to offset any loss of exports to the EU.

Does anyone really think that will be possible whilst at the same time rejecting at least the same trade protocols as proposed in a TTIP agreement?