How to calculate a mosfet's maximum usable amperage based on a temperature
This particular MOSFET is not guaranteed to switch 'on' very well with 3.3V on the gate. Suggest if your time is free put a bit less than 3.3V on the gate and measure Rds(on) for each part. Multiply that number by 1.5 and use that number for the 'hot' Rds(on), since it increases with temperature. Or just buy some better logic-level gate MOSFETs. 

You will also need to estimate the worst-case temperature inside your enclosure and pick a maximum junction temperature to operate at, and decide whether you are using the minimum recommended footprint or something better. 

For example if using the minimum recommended footprint and you want maximum junction temperature of 120 degrees C with a maximum ambient of  70 degrees C, then you can allow 50 degrees C rise. That's about 400mW allowable dissipation so if you are hoping to get 700mA you must have a cold Rds(on) with (say) 3.1V Vgs of about 0.54 ohm. It has a chance at that level, and a better chance at 350mA.