Other sampler designs; ideas
Combined pump/sampler: The availability of very small quiet blower air pumps opens up the possibility of combining the pump and sampler within one small case. The ones shown are 30 x 30 x 3.5 mm, 5 Volts DC, 25 dB(A), and are typically used for cooling electronics; they cost $10-30. They could (?) be powered by an inexpensive battery extender packs as used for mobile phones, cameras etc. The blowers typically draw about 100 mA, so a 5200 mAh battery extender (~$30 on Amazon) would last >24 hours (?). Of the models shown, one has a pressure drop of 0.25 inches water at 2 L /min, whereas another has a pressure drop of almost an inch of water. This is enough pressure for a sampler, although I don't know how they would operate with such low flows (overheat).
All this is said without any knowledge of the possible complexities.
The exhaust stream would need to be managed so as not to interfere with natural airflow around the inlet. Alternatively the pumps could be mounted external to the sampler case and attached by a clear hose, as is the current case.