I'm not sure that they would store them at PAE, though I suppose they could. Boeing is much more than just Everett.

737s are manufactured at RNT with final preparation for delivery done at BFI.

Test flights are done at several locations in addition to RNT, BFI, & PAE. Notably MWH, but also SBT, EDW, ROW, and other sites as well.

Still, if space is at a premium (or rents high), Boeing would likely store at MZJ which offers one of the most secure places to park aircraft.

Still given the demand for aircraft, the birds are likely to be sold quite soon.